biz,
You didn't say, but why do you want to go back to XP?
If you don't like the Vista user interface, Aero, you can set the UI to use "classic" mode, so that it looks and feels like XP.
And here's a concept that might boggle your brain, in kind of reverse-legacy situation, you might have a problem finding XP drivers for your machine. See, the component manufacturers had to build drivers for their newest Vista-compliant hardware, so that the computer manufacturers could sell computers with Vista on them (which is not the same as having a Vista-capable machine). Your new machine has Vista drivers. XP drivers may or may not be available for the hardware in it.
The only reason I bring it up is because, Vista is really more secure than XP, and in a lot of ways that users can't see. I think that if your machine can run it, and yours can, you're better off with Vista.