I called the Rent A Center they will redo my Windows XP free of charge
Mmm, are they going to give you a key this time? Just curious ;-)
Anyways, like everyone else has implied...read the fine print! It should be in there...if not, it's generally your responsability as a consumer to ask about it (though kind of crappy on their part). I'm not sure on the legality part--but you might be able to get some sort of reimbursement, but as far as the pirating goes, that'd be more on Microsoft's end. And even if it is OEM, I'm pretty certain it should have a key as well.
And as far as using it on another machine--well, if you really want to know the specifics, I'm sure you can read the license that came with it, and I'm sure it's on the CD as well as their web site. I'd guess it's licensed for one computer, but they might be the greedy foes like usual and try to say it should only be the the original computer--I'm not 100% sure how that goes, but I doubt it's worth worrying about. If Microsoft ever gets past all those who mass pirate their software--well, that's not going to happen, so...yeah!