Restoring XP on Windows 7 (within Bootcamp)

So I am currently running Windows 7 via Bootcamp 3.0 on a new 13 inch MacBook Pro running Snow Leopard 10.6.8. Turns out the Windows 7 disk I bought doesn't pass the Genuine Windows Validation... dangit. My question is, while I like Windows 7, am I able to (within the Bootcamp partition) use an XP restore (not a system disc) that I've kept, and revert the Windows 7 drive back to the XP operating system?

I know when I first ran Bootcamp 3.0, it stated that I must use Windows 7 and not a previous version. Is this possible? Or will I create a series of problems for myself?