Well, owners of R300~ or R600-based cards have some better luck: there're already quite good opensource drivers for these. :)

How is it possible to be a Linux netbook gamer if you enjoy games? Most good games in this world don't work right with Linux and most netbooks don't have enough power for them.

+1 for this.

I was about to suggest Linux too. But since I am hopeless with Wine configuration and normally just rely on vanilla version, I won't be much of a help if being asked about it. Still in this situation I'd suggest Linux.

I don't know exactly what do you call "good games", but anyway I have something about 20 games installed with Wine and about 30 native games here.
Well, half of them are quite simple (but still totally amazing: World of Goo, for example; or Machinarium… anyone?), but there're also 3D FPS', RPGs and RTS' here (full list will be long, but I can produce it if asked for).

As long as I understand that I'll never get SC2 or Crysis 2 (meh) running here, I'm still absolutely happy with what I have. Doubt if I'll have enough time to finish every one of these games in, say, ten years =)
Wine official site has a really great application database. You can usually find all needed instructions and how-to's for getting your game up and running.

Ironically, most problems with playing on Linux are caused by crappy DRM =)

Given those specs I'm assuming the graphics port is AGP? If so your motherboard may require an AGP driver. The default Intel chipset drivers would be fine for the motherboard but the default AGP drivers in windows xp are dumbed down performance wise and are only meant for broad compatibility and general use. Any application requiring decent bandwidth over the graphics port (like a game) will perform like ass with the default AGP port drivers.

You could easily get a couple gig of RAM for cheap to fix most troubles. I know sometimes it's tough getting older RAM modules, but the internet is a wonderful place, get some good deals, as long as you know the speeds etc, I'm sure you could get a couple of 1 gig sticks for cheap.

Your system is running slow with two diffrerent operation systems, also after a clean install? I would recommend to do a system check with different tools - cpu, memory, harddisk. For doing this best you can download a boot cd like Ultimate Boot CD. Boot your computer with the cd and make some tests, maybe you will see if a part is or getting defect.

After this I would take hands on the hardware - cleaining all the dust and start the system without external devices (printer, scanner, etc.) or internal cards (network, TV, sound, etc.) to locate a defect part.

512MB is definitely enough to run XP smoothly. To upgrade to 1GB brings of course a much better performance, but from your description it sounds not like a lack of memory. Also you can disable many services to get more free memory, for this you can use tools like ntsvcfg.

Edit: You can also change the Bios settings to standard, basic, safe, etc, if there is an option

As some people mentioned – quantity of RAM is NOT a problem here. From what you described it could be overheating CPU or failing memory. I suggest running Windows Memory Diagnostic (you can find it on UBCD) for 2-3 hours. It will check if entire installed RAM is operational and will put your P4 in some serious stress. Observe how fast benchmarks are running – if you get no errors from memory but stuttering benchmarks – CPU is your suspect. If you will run WMD without any issues – continue stress test on GPU. And how does your HDD behaves? If it is running all the time - check it with Victoria tool.

the config is good enough to handle diablo2 i finished the game first on a Pentium 2 i suspect the media center is draining your system resources try the home edition or other editions of xp

Did you installed all the drivers, didn't you?

I mean vga, sound, chipset, lan.etc.

Oh jeez so many replies.

I don't think it's a lack of memory. The computer used to be just fine all those years ago.

Drivers are all up to date, with the possible exception of the sound card as the manufacturer went defunct.

Changing XP editions is not an option. The license we have is OEM. Although it is possible to uninstall Media Centre as a component.

Heat and dust is probably the most credible thing so far. It's been sitting in one place for a good half a decade and it's never been opened. I should point out that it's an All-In-One unit and I'm yet to see a way to open it, but there must be a way.

I'll check on the dust first, I think. I'll report back soon.

Yep, just clean the damn thing.

I'm running those specs atm, using Linux (but used XP for many years without a problem).

The only thing I can think of is that the hardware might be damaged somehow. It seems to be a common problem with 478 socket motherboards that the capacitors would eventually die, but you wouldn't generally notice it until it was really bad. That's just an example, but that might explain why it is crashing, tho not necessarily why it is so slow.

Also, it might be overheating, which might explain why it is slow and crashing.

Not sure if this applies anymore but I remember that back in the old days you had to be careful to not put RAM with copper pins into a socket that had aluminium or tin, not sure which anymore, because that would start a very corrosive process. Check your RAM's pins and see if yo uhave any corrosion. Clean sensitive areas like pins and such with a Q-Tip dipped into ethyl alcohol, you know, disinfectant.

I would certanly advise to remove the cooler , clean the old thermal paste, apply a new compound and replace the cooler. Thermal compounds usually keep their efficiency for 3-4 years and then start to degenerate.