I have the same problem in Half-Life. I was using an old video card because my tnt2 broke and everything was working fine. Then I installed the Geforce2 GTS and the computer freezes now after 45-60 min of game play. This seriously annoys me because I am usually downloading something from hotlines... and besides I'm supposed to have an awesome computer!
Elsa Gladiac Geforce2 GTS
-Latest Nvidia drivers (6.xxx)
--Fast Writes Enabled - Could this be the problem?
256 MB Mushkin Cas3
1Ghz Athlon (with super cooling)
If anyone knows what the problem is please help.
Like I said, I had an AGP card before that worked fine... So it's not an IRQ conflict.