Hello, and welcome to the forums.
Your problem might be related to Vista or to how Kotor2 plays movies, as both have been known to cause problems. For Vista, I recommend you have a look at the FAQ and see if any of the fixes there work for you. You should also probably check the LucasArts Tech forum. For the movies, I can't remember all the problems and fixes, I'm afraid. A quick search yielded this, which might be worth a try. I'd suggest also doing a search for your video card etc. to see if others with the same components have found this problem.
I hope this helps.