Pop, I'm not an expert on this but I think if you've got a full boxed retail version of XP then none of the restrictions of an OEM version apply. You can re-install it on any number of occasions for whatever reason.
As long as it's only installed on one PC (and possibly a laptop, but I'm not to sure about that) then just get it revalidated. You can buy a new PC and still go ahead and use your copy of XP. Time and time again
At least that's how I understand it.