Discussion of anything that could easily be misused is illegal and not allowed on this forum. I very much doubt anyone will answer you in this forum. Sorry.
there are programs/ways to get it, but then that not the point. It is possible that jscam has a legit reason for his enquiry, maybe if he could tell us why he wants it?
its mentioned in the sticky, check the side of ur computer, normally winxp hologram stickers are put there, with the product key.
if, that is, your computer came bundled with XP