Can anybody help with my Doom 3 problem?

First off, my system specs:
Athlon XP2600+ on Biostar M7NCD (Nforce 2)
PNY Verto Geforce fx5700 Ultra
512mb 333Mhz DDR (single stick)
Windows XP Prof

Doom 3 crashes back to the desktop after a seemingly random amount of time. Somtimes it will crash after only a few seconds, somtimes I might get an hour out of it. After the crash, the following XP event log is generated:

The description for Event ID ( 0 ) in Source ( ) cannot be found. The local computer may not have the necessary registry information or message DLL files to display messages from a remote computer. You may be able to use the /AUXSOURCE= flag to retrieve this description; see Help and Support for details. The following information is part of the event: 7

I have tried loads and loads of things to fix this:
Switching between 4x and 8x AGP
Changing AGP apeture and disabling fast writes
Different detonator drivers including latest 61.77
Different nforce platform drivers including latest
replacing nforce audio drivers with latest realtec ac97 drivers
Taking out CD-ROM drive to improve power output (i have 350watts)
Even playing with case open to improve cooling

Any ideas?