I've been suffering from a very painful audio problem on Vista. Towards the end of all my songs the sound would suddenly start to skip and the sound would be very jittery for the last 20 seconds or so.

Initially I put it down to driver issues but after installing new ones, the issue still occurred. I got annoyed and eventually stopped playing a lot of music at work in my office. I finally had enough the other day and a quick Live search later a resolution appeared "turn off sound enhancements":

http://help.lockergnome.com/vista/windows-media-player-skips-ftopict36704.html

No more skipping and I'm much happier!