I know I should probably post this under a pseudonym to save my blushes, but... Now, if I was selling a copy of OS X then it'd be easy, I'd just sell it. But This Windows XP lark has this activation crap that I'm thinking could potentially cause problems. Brief outline. A client gave me a PC in 2005 to carry out cross-platform development work on a project, now the PC has long since died, and I'm left with the Window's XP Upgrade disc, as well as most of the packaging... including the the 'Product Key', and the 'Certificate of Authenticity' from the box itself. Now, as far as I'm aware, my client has new PC's, with new versions of Window's on them, I now own this copy of XP, though it's no longer in use on any machines. So... Can I sell this? Can the buyer just use the existing 'Product Key' or will that cause problems? Or do Microsoft issue another 'Product Key' to the buyer, because they'll now own the copy of XP and have both a 'Product Key' and 'Certificate of Authenticity' to prove it? Any idea's?