Comprehensive KnowledgeBase article from Apple regarding the Boot Camp public beta. Includes an explanation as to why it requires a full installer for Windows XP SP2 or later, and also this regarding music from ITMS:
I have purchased music and video from the iTunes Music Store. Do I have to authorize my computer in Mac OS X and in Windows XP?
Yes, you need to authorize one computer for Mac OS X and one computer for Windows XP if you wish to play music or video in both operating systems, even though the operating systems are installed on the same computer.