Originally posted by Awimoway
Not sure I understand all of your question. It is true that you can only play iTunes music on 3 computers, unless of course you burn the AAC files to a disk as AIFFs and then rip them a fourth computer. But you'll lose some sound quality of course.
Anyway, all you have to do when you copy protected music to another computer is authorize the music for that computer.
What I don't know is whether you can re-download directly to the 2nd and 3rd authorized computers from iTunes music store. I read a review of iTunes for Windows, and the reviewer said that he couldn't do this. But maybe on Macs this is different.