My guess also would be overheating. Ive got problems with the same card about 2 years ago unfortunately it has been solved by replacing the card with one from different manufacturer.
The funniest part was that the original card had fan and the replacement was only with passive cooling in any case the second one was much better.
A quick fix would be using rivatuner and underclocking the card. alternatly you could add a fan or upgrade the curent one on the card.
i am running the FX5500 is not a bad card cost me £45 new around 90USD
stays pretty cool however it crash's with NFSU2
this is the second time i have came across this issue now another guy playing americas army with the same card had some nasty screen coruption.
i recomended that he changed his driver version from newest to the 78.01
I say this because each update of the Nvidia drivers adds a new card and there are slight difrent methods of working ie a driver that suits a 7900GT will not nesecerialy suit an older fx model. i am personaly running the 78.01 with out any issues.
I had issues with older cards running newer drivers ie my old 460MX
wouldnt run worth a damn on anything newer than the 7*.** driver versions but using anything from 28.04 to 69.** worked prefectly.
Always read the update info on the updated drivers if in doubt dont bother with them.
This maybe common sense but i have made mistakes b4 and had 2 reinstall windows because of it... only human after all..
I hope this makes sense i am pretty tired after all.
If this didnt happen before then i would suggest looking at your temps as this is a common sign of the gpu over heating, I would update the drivers anyway because that can only do good.
I was gonna buy a rig with the e6700 + 7950 gx2 but then i relised that direct x 10 is coming out. So now i am gonna buy a laptop on the cheap work with that for four months then get my self a super kick ass rig and leave the suckers that are buying now behind.
This way teh price of Ram the motherboard for the new dual core processors and the Cpu will all come down in price nothing but good.
i had the same problem before with my FX5600 nvidia card, i started to see polygons on my screen after creating a profile and customizing the video settings. what i did was i reinstalled the drivers and didnt changed or customized it anymore and i deleted the profile that i made.
oh btw, dont forget to download the updated driver from nvidia.
Is driver are updated and installed successfully?
I'm sorry to say but Nvidia is a very good company today but they really sucked when they invented the so called great FX series. I would say the best opition would be to replace it with a nvidia 6 or 7 series if your a gamer.
Problems could be like others have said overheating. Out of date drivers and other stuff. You should also check that it doesn't take more power then your powersupply can give.