i am looking for a way to create practice loops from songs in my itunes library. can anyone point me in the right direction for mac supported software for this application. is there a way to use garage band for this?

i'm a giant fan of 'amazing slowdowner.' it'll loop, speed up or slow down, and pitch change (or not) your tracks. a great transcription and study tool, and useful in sound design as well.
good luck.

An even better app for transcription and slowing down music is Transcribe! It's simply the best out there for that. You can set up a perfect loop and export it. Also try the Apple Loop utility (Part of Logic Studio). You can create your own loops that will adjust to tempo and key (within a reasonable amount) in Logic or Garage Band.