Sampling Internally with a Mac

Hey guys, another quick question. Is there anyway I can sample internally, i.e. sample audio playing back through my Mac, i.e. from iTunes or Quicktime, audio from you tube or other audio on the internet?! I'm using a Mac, with a Digidesign 002R. Is there a way this can be done with the gear I currently have or do I need to download additional software to achieve this. Any advice would be greatly appreciated. Thanx a lot.