This article was originally posted on Team Tutorials, here is the original article.

This is a rather simple way to recover a key for a Windows installation that has gone bad. Especially useful if you need to re-install it but don’t have the key at all too!

1. Open up regedit first of all.
2. Get to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\Current Version\
3. View the key DigitalProductId
4. Write (copy won’t work) bytes 34 through 42 down
5. To decode it, go to Dagon Decrypter.

Viola! You have the XP key ready for use again.