In my experience XP drivers are still in abundance, my hardware includes a one year old Epsom printer/scanner, a Nvidia GTX 570, and a four month old logitech K360 keyboard.
I can honestly say that i have never, to this day had a problem finding XP drivers.
Im no expert but i'd say that you need to format your hard drive before installing XP from start, as i don't think Windows 7 would allow installation of a predecessor over itself. 😉