Moses,
It is very easy, because Apple made a software just for that which burns a CD with all the drivers needed and installs them in XP. You have to update the firmware of the mac to the latest version too. Every thing is explained with that
bootcamp software. You have to have your own XP install CD too.
For the little story, there was a challenge with a $13,000 prize for who would find a way to boot XP on a mac first. It was not trivial, because the new macs use EFI, and XP does not. The challenge was
won, and shortly after, Apple came up with their own official solution.
Also, this is not an emulation. Indeed, XP runs native while OS X does not because large portions of it are still written for the PPC and translated for the Intel processor by the Rosetta engine. Now, when you think that one can use this trick with a $599 Mac Mini, it really opens horizons...
Aurel