google Agent Ransack... Tell it to look for files/folders created when you installed the game (orginally)...
Of course, have you tried Windows SYSTEM RESTORE function?
Start > All Programs > Accessories > System tools > System Restore
Set the restore point 1 day before you installed the game.
Also, I'd recommend a video card upgrade when you can. At least a GF7600GT ($130) for this and other games. 7600GT is about 5-8x faster, allowing you to crank up the resolution and graphic details.