In iTunes 3, you can cut up songs by setting the start and end times. Start by control-clicking a song, choose Get Info from the contextual menu, then go to the Options tab and choose a start and end time and hit OK. Next, from the Advanced menu, select "Convert selection to MP3." iTunes will make a new song (leaving the old intact) based on your chosen start and end times. This is great for those tracks that contain two songs.
[robg adds: I used this trick to split apart two or three of those silly "hidden bonus track" songs -- you know the ones with five minutes of silence and then the hidden song starts? Now, finally, I have the hidden song as a 'normal' song without having to fast-forward through the silence. This hint saves a trip to and from QuickTime Pro to accomplish the same result, which I was usually too lazy to do!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030325150107605