Vista - Sound stutters in Media Player in full screen

Because I was getting such miserable performance from Media Player in Vista,
I downloaded the NVidia pure video codec to try it out. It improved things a
bit, but when I go to full screen, the sound begins stuttering badly, and is
also not syncronized. In XP everything plays smoothly. I can't figure out
why there is such a problem playing avi and mpg files with Media Player.
Same thing occured in Media Center. Anyone else with this problem? Or anyone
who is getting good performance from Media Player and Media Center? This
could be what keeps me from upgrading to Vista, as I use my computer a lot
for video editing and producing.