There are currently three ways to run Windows XP on your Mac.
Boot Camp - Apple has officially released its own version of Windows Boot software. Code-named BootCamp it allows users to boot XP and Mac OS X natively on the same computer. The only thing that is required is your version of XP and the BootCamp Installer. Read about it here .
Share your installation and integration tips/FAQs at the Boot Camp OnMac wiki page.
XOM - This is an open source solution. It was the first solution, produced by Narf and Blanka.