Well, if I remember correctly, Windows XP ties itself to the Hard Drive and Motherboard, meaning you may have to buy new ones. This happened to me, but don't take my word for it. Check in with your local "tech guy" to see what you'll need to do.
The Windows XP license is tied to a specific system only if you buy it from a vendor like HP, Dell, Lenovo and others, but not if you buy your own copy of Windows XP. Regardless, the OP has to buy a copy of Windows 7 64-bit, but new hardware definitely isn't required.