|What problems are you having with Vista?|
Do you have a genuine Windows XP cd? (not a manufacturers brand name, like Dell, Acer, HP etc.)
If so does it have a Service pack included SP1 or SP2, required for sata drive support.
Chances are your new computer is fitted with a sata hard drive, drivers will be needed at instalation.
Drivers for all your hardware, motherboard, video etc. will be needed, which may or may not be available.
Others may add what I've forgotten, while it certainly is possible to do, it may be a pain in the rear.
Learning to get along with Vista may be better in the long run, unless you have specific needs for XP.