If you've been tinkering with the Boot Camp + Windows XP on the Mac, you'll be happy to hear that Apple has updated the suite and moved it to Beta 1.1. Aside from adding support for the Xeon-based macs, the updated Boot Camp adds a host of new features such as the ability to install XP on any internal HDD, better replication of Windows mouse events, support for some Mac hardware and other updates. The Boot Camp itself is free, though you still need a license for Windows XP to install it (legally).
A lot of Mac enthusiasts were disappointed with Apple's decision to un-officially support XP on the Mac, but so far as a whole people have been loving being able to try "Windows on a Mac".