"The Magical Jelly Bean Keyfinder is a freeware utility that retrieves your
Product Key (cd key) used to install windows from your registry. It has the
options to copy the key to clipboard, save it to a text file, or print it for
safekeeping. It works on Windows 95, 98, ME, NT4, 2000, XP, Server 2003, Office
97, and Office XP. This version is a quick update to make it work with Windows
Server 2003."
Magical Jelly Bean Keyfinder
http://www.magicaljellybean.com/keyfinder.shtml
A word of caution: If you have an OEM system, the existing product key may not
be the one required to reinstall the OS. If this is the case you should use the
product key found on the label attached to your computer's case. If the label
cannot be found, contact the OEM manufacturer. If the system has already been
reinstalled using the proper product key, this is not an issue and the keyfinder
will reveal the correct info.