Correction to above poster: NOTHING works on Vista. I'd suggest right clicking the shortcut, then selecting "Run as Administrator". --- Extreme Demon: "Teamwork is not getting revived every time you die."
For KotOR I, I set it to Compatibility Mode for XP Service Pack 2 and Run as Administrator and I haven't had a single problem with it since. KotOR 2 is trickier... I had to install a hacked .dll to get it to work every time. You can make it work on Vista... It's just more of a pain in the rear than it should be.