Quake engine problems

I have been trying to help a friend of mine sort out a problem he is having with games using the Quake engine on his PC. I suspect it may be video or GL drivers, but he has installed an Audigy Platinum recently and that is when the problems started. His specs are:
Gigabyte GA-7VAXP motherboard
AMD XP 2GB
256MB 266 DDR RAM
30GB Fujitsu HDD
Audigy Platinum internal sound card
Leadtek Ti4200 64MB video card
DirectX 8.1

When he starts RTCW it hangs at the point after the engine initialises when the first blank screen before the publisher logos come up and the machine needs to be rebooted. The same thing happens when we try Jedi Knight II and The Thing. In addition, Mafia also runs at about 10-20 FPS.

I have reinstalled Windows and everything from his original driver disks to try solve the problem. Is there any command-line parameter we could type to isolate the cause of the problem or perhaps a utility that would let us know? He is reaching a point where he is ready to give up on PC gaming altogether.

Thanks in advance to anyone who can help.