If for some reason there isn't a product key sticker on your computer...
WinkeyFinder.com - Win Keyfinder 1.73 RC2 - Find Windows XP CD Key - Windows Vista CD Key - Change Windows XP CD Key - View MS Office CD Key - Change MS Office CD Key
Run that and it should give you your product key.
WinkeyFinder.com - Win Keyfinder 1.73 RC2 - Find Windows XP CD Key - Windows Vista CD Key - Change Windows XP CD Key - View MS Office CD Key - Change MS Office CD Key
Run that and it should give you your product key.