If the machine was Boot Camp capable already, you should be able to slip the XP-SP3 disc and have at it. All it requires is that the EFI be able to emulate BIOS in order to boot the installer disc. You really should have the Boot Camp drivers handy though-but I don't see that as an issue-use any of your recent OS X discs for that.
The only tricks or tips I can think of are all off of the Windows XP installation and use playbook. Install an antivirus package right away, even if you're just playing games, because any Internet connection can be dangerous to a Windows machine.