A standard T5720 probably isn't going to cut it as a HTPC unless you're going to use it in the manner HP intended and stream all content off a server, so lets go through the upgrading process.

The T5720:

I don't know about you but I think it's a groovy little box that wouldn't embarrass by living under the telly.

As mentioned; six USB ports, 1Ghz GeodeNX (Athlon XP) CPU, up to 1Gb of memory, PCI header, 2.5" IDE header.
That's enough to get started, though I suspect most will want better GFX than SIS's integrated offering and I'd upgrade the BIOS as soon as possible.

So let's see what's a-lurking inside. Unscrew the two cross-head screws either side of the rear panel, then slide the whole top cover toward the rear about 1/2 inch. The cover should then lift off. Do note the motherboard speaker is in the lid so remember to disconnect from it's header carefully.


Here, the Flash module and Memory have been removed.

As we can see top-left there is a standard 2.5" IDE header - pin 1 is marked as '1' in the photo. Like all IDE headers it's just push-fit but take note of the plastic support pillar - the lug on the top either needs compressing or cutting off before the Flash module can be removed.

The memory is a standard DDR PC2700 SoDIMM. Usually 256Mb (not enough), 512Mb (just enough), or upgradeable to 1Gb (enough).

As can be seen the CPU and motherboard Chipset live under groovy passive heat-sinks which are remarkably efficient as we shall see later.

Remaining areas of note are the CMOS battery, the PCI header, the speaker header (you found earlier), and that BIG capacitor (bottom-left) - more later.

Off with the Coolers:

Just to be awkward this photo has been turned clockwise by 90 deg.

At the top we have that GeodeNX 1500 - It really is just a re-badged Athlon-XP, and it's in a standard 462-ZIF socket. Hmm, good. That means, space allowing, one can use an active Socket A Cooler for better heat dissipation if you really upgrade it.

Both heat-sinks are attached by four spring-loaded screws. I can think of no reason to remove the Chipset cooler but if upgrading the CPU I'd suggest the following:
Remove two opposite screws first. Then progressively relax the remaining two until it pops-off - you really don't want uneven loads on that delicate CPU.
Reverse the process for reassembly - you can't over-tighten the screws. Don't forget to clean off the old thermal compound before using a good replacement.

The motherboard has no fan-header which we'll need to sort for CPU upgrades. Also I've yet to find any software that will give a useful reading for CPU temperature - more later.

Now for Some Upgrades:

To the right is my T5720 complete with HP's expansion dock and vertical stand.
In this form it's a more substantial bit of kit but is still pretty small while allowing room for more goodies.

The upgrade comes with a PCI riser and a rather deeper lid to accommodate the PCI card of your choice. It fits exactly as the old one but has an extra screw to retain said PCI card.

With GFX card and HDD it is a bit tight in there but the 2.5" HDD does fit without further modification. I have covered the long ends of the drive with tape to reduce the risk of shorts. Maybe a GFX card with a passive heat-sink would be nice but this one isn't too noisy.

Fun with Modding:

The above upgrades plus a few USB bit's 'n bobs will get you all the HTPC you need, but why not take things further?

First on the agenda could be the CPU. The 1Ghz NX1500 is fine, much faster than an equivalent VIA, and very close to a 1.6Ghz Atom, but more speed is always nice.
The 1.4Ghz NX1750 would seem logical but will the BIOS recognise it? Will the passive heat-sink cope..? The NX1500 puts out 6W while the NX1750 puts out 14W. AMD do recommend a fan for the NX1750.

I'm pleased to say the BIOS recognises the faster chip at the correct speed, though it calls it a GeodeNX 1700 for some reason. The heat-sink is a very good design but I would go along with AMD and add a fan. Especially with no way to monitor CPU temp.

Power for the Fan:

The T-series motherboard was never intended to support active cooling so some ingenuity will be needed.

The clever thing would be to use a multi-meter to find suitable power rails and solder in a header at a convenient spot. I've not done that for a couple of very good reasons:
-Why mess about looking for suitable lines and run the risk of frying my motherboard when I know where suitable power can be found?
-The motherboard was made to pesky RoHS guidelines which means nasty lead-free solder which is a bugger to work with using hobbyist equipment.

My suggested solution is to solder flying leads directly to the inside of the external power connector. It's a bit fiddly being hidden behind the big Cap in the photo, but there's two suitable metal tabs - one on the end, and one on the side.
Clean the connectors, dab with flux, then 'blob' a little solder from your iron on to each one. You can now solder in the wires.
The fan won't be under power-switch control but it will remind you to unplug after use.

Mount the Fan:

There's nowhere to mount a fan internally to blow across the CPU's heat-sink but I have a cunning plan.

There is room in the base, which has nicely sized holes in it. In the position shown a fan blowing upward across the coolers will augment the natural airflow as HP intended.

The process is simple enough. Take a 12v 40mm fan and super-glue it to the base as shown. One of the cross-pieces will need removal first.
The flying leads soldered to the PSU plug can then be fed through the bottom of the case and plugged into the fan.

I have run my T5720 with a NX1750 for many hours for a good speed boost with no stability issues at all. It's reasonably quiet and not too warm.

More Speed!!!:

I have a 2Ghz Athlon XP-M. Will the BIOS recognise it? Will the motherboard support it? It would, of course, be foolish to try without upgrading the cooling.

So expecting escapes of magic smoke, an over-loaded PSU, and maybe flames, I tried anyway. I did fashion a little air-flow tunnel to go over the CPU heat-sink - it made me feel better.
It booted!
The F10 BIOS screen called my XP-M a 2000Mhz NX1700, while the TAB screen sees a 2000Mhz Athlon. Nothing broke, I watched two movies, then did a bit of surfing at which point Google Chrome got a little flaky - oh, and the computer was nearly too hot to touch!

The reason for this miracle is the mobile Athlon (XP-M) is rated for 90-100c, but it's still not a good idea. Moving on...

Do it properly:

It's good to see a T5720 will support any Socket A CPU but more than a NX1750 really should have a proper active cooler along with upgraded airflow.

Here we see the only half-decent cooler I can find that should fit in the box. An Akasa AK-351-2. With a total height of 35mm it's nice 'n stubby so will fit under the GFX card, it even blows air across the the HDD.

Of course a cooler this small isn't going to be amazingly efficient so a heat tolerant CPU is still a good idea. As is making sure case ventilation is as good as possible. Ho, hum two fans wired in to the PSU.

My little Thin Client come Media PC has closed on my water-cooled gaming rig of a few years ago. Ok it's still 500Mhz short, there's no 2Gb of dual-channel DDR500+ RAM, no DFI Ultra-B motherboard, and the GFX card isn't up to much (there's better). But it's cheap to build, wife-friendly, and I've had fun along the way.

As can be seen the system is quite able to take a (very) low profile active cooler. I did have to replace the full-height fan with a (louder) slim-line one to fit under my full-height GFX card - if a low-profile one is used a taller heat-sink would fit just fine.

As an added bonus removing the original cooler will allow internal fitting of a quieter and more efficient 60mm fan. This was done by the expedient of 'gluing' it down with BluTak and then sticky foam pads front and rear to keep it central - take care to keep some clearance front and rear so the cover doesn't touch the fan blades.

Power for the fans is taken in parallel from the same 'bodged' header as before. Each fan had a 10-20R resistor soldered in to slow them a little and reduce noise. Initially I wired them in series so each 12v fan got 6v but with a lack of temp monitoring I worried this slowed them too much for comfort.

This arrangement seemed to work fine but with all the extras the PSU got a bit toasty... So I fitted lower power fans without resistors. Good for the PSU, fingers crossed on the CPU front.

A Better Graphics Card:

At this point one really has to ask one's self 'Why upgrade any further?' The system so far will have no problems with general HTPC duties, even a little very light gaming and emulation would be fine. To be frank the T5720 didn't need a CPU upgrade to fulfil this role. Still, once past the basics half the fun is seeing how far you can go...
The Geforce 5 really isn't a great graphics card but it does have the advantage of being cheaply and easily available while having a very low power-draw. Somewhere in the range of 10-15W.

The PSU itself is only rated for 50W so is already being pushed by current upgrades. If any further hardware upgrade requires more power the PSU will also need replacing.

Traditionally the 'daddy' of the PCI GFX cards is the Sparkle SP95GT1024D2L-HP shown above. It's a Geforce 9500 with 1Mb of RAM and mercifully a fairly low draw of about 50W. A decent card and though too much for our PSU it is at least feasible to shoot for with available 150W power bricks. The problem is such cards are almost impossible to find. A Geforce 8400GS or 9300GS may be a more practicable option.

Can we do better?
HIS make a Radeon 5450-based PCI card as shown to the right. It ticks all the boxes with excellent output options including VGA, DVI, and HDMI plus hi-def sound. It's power draw of 10-15W is very good with silent operation and probably the highest spec GPU we'll ever see in a PCI card.
At the time of writing it is in production but availability is sadly restricted to very few countries: Canada, Norway, USA, and some parts of Asia.

The End Result?

Assuming I can leave well alone to the left is the 'final' version.
The GeForce 5 GFX card has been replaced with a Sparkle SP95GT1024D2L-HP PCI. I'm in the process of converting my film collection to smaller H.264 MKV's to save space thanks to the built-in codec acceleration. Not that a 2Ghz Athlon wouldn't cope but it seemed like a good time to go ahead.
The use of a low profile card has allowed for a taller and more efficient 60mm fan on the CPU heatsink. Better still it's an AcoustiFan DustPROOF bought from Silent PC. As a result my HP HTPC is once again almost noiseless. I also repalced the 60mm 'case-fan' with a much quieter 40mm one I had laying about. The mounting solution is as before BluTak and sticky pads.
I also split the ribbon cable for the 2.5" hard drive round the fan to help with airflow. It's an easy job to do but it's important not to cut any wires. Don't use any kind of sharp blade! The end of a screwdriver or similar will do to part the plastic without harming the wires.
I'm pleased to say it's now really quite acceptable for light gaming along with HTPC and emulation duties.

Not yet!

Maybe this is the final, final version...
While the Sparkle card is indeed excellent, the whine from the miserable little fan on it's active heat sink was getting to be a proper annoyance. It wasn't all that bad but as this is supposed to be a quiet HTPC it was just too much. Also, in spite of the upgraded PSU I think the G-Force chipset was drawing too much current for the PCI bus in this machine. It started getting random lock-ups and occasionally on boot wouldn't recognise the card as anything other than a generic VGA - power rail flakiness in other words.
Oh, well... A good excuse to find that PCI Radeon 5450-based card I mentioned before. Happily the card is now available in the UK under the Club brand. Mmmm, much less power draw, no whiney fan, even better graphics, and via the HDMI connector I've got full surround sound!
Happines is a Club RADEON HD 5450 PCI edition. :-D