I think that if you want to boot camp your Mac you're going to need to bite the bullet and install Leopard. Bootcamp Beta is no longer available from Apple.
The only other way to install XP is to purchase a product like Parallels or VMWare, but if you're going to spend the money for them you may as well go the Leopard route.
Amazon.com has it for $20 less than the Apple Store, plus free shipping. I would recommend that path anyway, as boot camping with Leopard is incredibly painless (easier than installing Windows on a regular PC).