I had exactly the same problem as you guys...the game would run for 5 to 30minutes and then the video would lock up along with the sound. I could not control alt del to exit the game, I had to reboot each time.
Now here's the strange bit
I had a similair problem with TRD with a ti4200 256 X8 which was overheating and causing the game to lock up. I enabled AA and AF to X2 and the lockups stopped. I used the same "trick" with prey on a completely different rig and guess what? No more lock suey!
Strange....but true.