I have had the exact same problems. I updated my video driver to the latest one (ATI 8500 AIW) and that has helped some, which makes me think it could be video related.
I ended up uninstalled itunes 7 and going back to 6.05
Ever since I updated to version 7 of iTunes, I'll occasionally get choppy sounding playback. I thought it was a RAM issue at first, but then I played a song (Why Does It Hurt When I Pee? by Frank Zappa to be exact) with only iTunes open, and it still was choppy. And this is happening on a brand new laptop.
this problem peeses me awf! Has anyody else experienced this?