In a recent case of “borrowing” at work the product key for my Windows XP Pro installation went for a walk and never returned. I was staring down the barrel of a $100 bill to purchase software that I had already purchased once because of this.
Thankfully I was able to find the product RockXP. Rock XP is described as such:
RockXP allows you to retrieve your XP product key that you used when you installed Windows XP, as well as keys for other Microsoft products. This can come very handy if you need to reinstall but have misplaced or lost the CD cover with the serial sticker. In addition, the program also lets you save the product activation to a file, and enables you to recover usernames and passwords contained in the Windows Secure Storage.
One of the best things about the product is that you don’t even have to install it, it is a standalone application that just runs. I was able to recover my product key and will be able to re-install Windows when the time comes (which looks to be sooner than later).