The only preparation you need to do is to make sure that the drive you want to put Win XP onto has enough space. I don't know how many Gig it needs, but the box or MS website should tell you.
Then you simply start the install process using the XP CD. Be sure you opt for new install, not update (or upgrade, or whatever the option is). It will then note that you've got another version installed, will ask you which drive you want to put XP on, and create a boot-up file that gives you the option to select which OS to use every time you boot up.