Chances are your Laptop came with a restore partition. That means part of your hard drive is set aside and has Vista on it. All you would have to do to reinstall is press a certain keystroke during boot. For my HP it happens to be f11, but I'm sure your user manual will tell you.
As far as I know Vista and Xp drivers aren't going to be compatible, but I guess it can't hurt to try. Worse case scenario is you may be stuck with Vista.
As far as the preloaded stuff goes, you are just out of luck unless you want to purchase another copy of vista. That's one of the downsides to buying a prebuilt computer.