It is possible, but as you have bought a new computer with Vista installed, it is possible that drivers, etc will not work with XP.
It is far easier to keep Vista on one machine and use that system.
It is a lot easier to use than XP anyway, so you should have no problem.
I feel that to dual boot on a new machine, would honestly be more trouble than it's worth.particularly as you say, it is built to run Vista.
I happen to be one of the few, who like Vista, and would not go back to XP.
All the best.