iTunes skipping to the next song before the current song is done playing

So, ever since I upgraded to Leopard and put all of my music back onto my computer, I've noticed that my iTunes will skip to the next song before the current song is done playing. And it's not consistant between songs... some songs will do it early on (<10 seconds) some songs will do it later on in the song (>1 minute) and some songs won't even do it at all. I reinstalled iTunes to see if that would fix the problem, and it did not. So, what's the deal? Could there be something wrong with my music files? HELP ME!
-Aaron