My system is similar to the one listed in the OP. (7900gt, Opteron 144, WinXP)
Using the lasted NVidia drivers would cause some spell effects to make big blank rectangles appear on the screen. Turning on both Software Blitting and Transperancy would fix the visual artifacts, but make the game run at a crawl.
I found installing the old 56.72 drivers (from 2004) fix the spells and make the game run at normal speed, however it also makes the computer usless for everything else. So tommorow morning I'm installing a second copy of windows onto an old hdd specifically for running PS:T with the gimp drivers.
The hoops we have to jump through to get old games to work eh?
