Display corruption

Hi I have this display corruption issue for about 2 weeks now, I suspect it is the graphics card but I'd like to be sure before buying a new one. My computer specs are these:

-PSU Tacens Valeo Pro 600W (I guess this brand is unknown outside southern europe but it is overall a decent psu, nothing like a generic one)

-Motherboard gigabyte ga965p ds4

-CPU C2D e6600

-2x1GB kingston valueram modules at 667

-GPU G80 XFX 8800 GTS XT 320 (this is a slightly overclocked version of the normal 8800 gts, I haven't done any additional overclock)

-SO WinXP SP3

The corruption starts at the bios screen and is very similar to this picture: http://www.playtool.com/pages/arti [...] emory3.gif but its pattern and colour varies depending on the resolution and whats being displayed on the screen. Also windows won't load with drivers, I have to start in safe mode or uninstall drivers and disable hardware acceleration or windows will hang on loading screen.

I have run memtest for more than an hour without errors , cpu stress tests with no problems too and I think it isn't the psu or motherboard.

Also after a week of running the computer without video drivers the corruption started to disappear at longer intervals each time until it was completely gone, I tried to reinstall the drivers and to my surprise the gpu was working again, I could even play demanding games without problems. That lasted more or less a week then the corruption reappeared, isn't this weird or just a symptom that the gpu is dying?

Well I forgot to mention a few things; the card has been working in this computer for 2 years without problems and I've checked all the connections. My theory is the card's memory was damaged from overheating, I usually checked temps from time to time and they were ok but after the corruption was gone and the card worked again I checked the temps while running atitool and demanding games with vsync and they would go over 90C while in less demanding games without vsync (like team frotress 2) temps would stay in mid 80s. So I unmounted the card and noticed the fan was full of dust, I've cleaned it and temps won't go over 90C while running atitool but I didn't notice this before and I've been playing games with vsync for a few months so I guess the prolongued use of the card at that temp might have damaged it.

Anyway I've alredy ordered a gts 250 and in case it's not a gpu problem I still can return it since it's an oem version. Do you think my cpu would bottleneck the gpu? considering I'll overclock it to 3.0 and that I play at 1680x1050?

Yeah I hope so, the 8800 was alredy struggling with never games.

I'm wondering if you can load windows xp normally without a graphics card? I was thinking to remove the 8800 gts until I receive the new one, I can't control the fan speed and it's just creating unnecessary heat and noise.