OEM copies of XP, like the ones that come with computers, are legally bound to the hardware they came with. You'll have to buy a new copy of XP or use an OS like Linux that's free.
I have an old computer with XP Pro pre-installed on it. The computer came with a 'Restore Disk' that refuses to work on any other computer.
Is there any way I can install and activate that copy of XP on another computer? I can buy a 'barebones' computer quite cheaply with no operating system installed, but can't figure out how to re-use the XP from the computer I'm going to discard.