I have the same problem as you guys do...
1. OS Xp sp2 pro
2. Video Card Asus fx5600 256td (brought it about 4 years ago... not that old)
3. Problem occures while playing games only (GTA:SA, Portal, HL episode2)
4. Never had this problem before... started like 2 month ago
First it was bearable somehow it occured once in awhile but now its realy annoying its happen like every 5 minutes...
My video card is updated I checked it and I was using this driver before so im guessing its not the problem.
Direct X version is 9.0c and the games are running just fine so guess its not that too...
So I have to agree with what "Kissker" said it must be some hardware problem maybe its overheat or something
btw aitken325i I have tried to minmize the video setting already and its doesnt helps
P.S Im tring what "Kissker" advised about the trouble shooting option than ill try few others things if I get any luck ill let you know guys