Doom 3 problems (possible overheating?)

[Da Reaper]

Hi, I recently intstalled Doom 3 and have had a problem with running it. The game loads fine, I can get into the game and run around, however, after a few minutes the display goes haywire and I end up with something like this: http://seizure.t35.com/d31.jpg and when I escape to the main menu, I see this: http://seizure.t35.com/d32.jpg . After exiting to the desktop, the problems continue: http://seizure.t35.com/d33.jpg . I have tried downloading the new ATI drivers, and have used the edited the DoomConfig to smooth the texture loading process, so I suspect the problem lies in overheating, but I'm not too sure. :S

System:
Athlon 1.8 XP
ATI Radeon 9600
768 Mb RAM