Something, that seems to be very strange: you lost your CD Key for a WinXP installation CD. You might think you could loose the CD, too. Wrong. Just follow the lead on http://ehacks.wordpress.com/2008/01/11/how-to-find-your-windows-xp-produ... and voila there you go.
http://sirio.isgarnet.net/facepalm-leo.jpg
At least it worked for me.
Have fun!