Does XP come pre-registered on HP systems?

I recently purchased some equipment for my business which came with a HP dc7600 computer that I do not need. It's sitting here still in the box. I'm thinking about parting it out for use in other computers around here. My question is, does HP pre-register the WinXP Pro on the computer before it's shipped? And is HP the same as Dell where the OS will only operate on a Dell or HP machine? I would like to upgrade my system to XP Pro if possible (I can always put Win2K on the HP).