BleepingComputer.com: Laggy Sound On Itunes

So I play my music through itunes, but onces I open a new program such as Windows Media Player to see a video, or if I'm playing a game, the sound starts breaking up, but it seems like it plays half a second, then skips to the next second, only to play half of it, ect ect. Hope that made sense.
What I was wondering: Is this a problem with my computer, my drivers, software, or what. It's SO annoying =[
Is there some type of...Optimizer I can get?
I got the dualcore optimizer from AMD, and I've tried changing what CPU's things are executed from..but nothing seems to work. It calms down SOME when I put it on only one CPU.