Do you have a retail version of XP? OEM versions are not transfereble. In addition you would need to find XP drivers for whichever pc you used to install it on.
Then there is the problem if said pc has a SATA hard drive you would need drivers for it on floppy disk from the motherboard maker before you can install XP which would have to have at least Service Pack 1 incorporated in it.
If the pc is in good working order why mess with it.