na man... u need better cooling coz UT is making ur CPU work for a change ;)
Ive got a P4HT 2.4 GHz, with 1 GB Ram and UT2004 on XP never crashes and I play for hours....
But my case has 7 fans and vents on top, front, back, and sides.
It sounds strange, but yes, take the side off your case, maybe even put a desk fan next to it, and see if that stops your problem.
Also, try checking your CPU temp in the bios. My PC runs most of the time at 25C.... thats sweet but only because of all the fans and the unit is ON the desk... used to reach 45 when it was UNDER the desk. AIR FLOW my friend.
I log on, therefor I am.