There are some limitations with installation of XP/BootCamp on compatible Mac hardware. The complete manual is at the link and an excerpt is copied below for quick reference.
http://manuals.info.apple.com/MANUALS/1000/MA1519/en_US/Boot_Camp_Install-Setup_ 10.6.pdf
What You Need
An Intel-based Mac computer with Mac OS X 10.6 or later
The keyboard and mouse or trackpad that came with your computer. (If they
aren’t available, use a USB keyboard and mouse.)
Mac OS X version 10.6 or later (the latest version of Mac OS X is strongly recommended)
A built-in optical disc drive or a compatible external optical drive
A Mac OS X version 10.6 installation disc
One of the following:
- Windows XP Home Edition or Professional with Service Pack 2 or later (32-bit version only)
- An iMac or MacBook Pro introduced in 2007 or later
If you’re not sure when your Mac computer was introduced, see http://www.apple.com/support/hardware, click your Mac model, and look for an article on identifying your Mac.