XP Key from recovery CD doesn’t work

Hi,
I’ve got a Dell pc that died so I tried using the XP Pro recovery disk to upgrade my Gateway to XP. I misplaced the key so I used the key from my other Dell to get it up and running until I found the original key. Ran across an article on pulling the key from the CD itself, which I did find in the Unattend.txt file on the CD. Attempted to reset the key to the correct one as noted in the Techrepublic article “Get IT Done: Change the product key on Windows XP”, but it keeps telling me “incorrect product key”.

Do I have to go back and reinstall Windows XP using the correct key from the CD from scratch or is there a way to fix this without going through all that trouble?

Thanks,
Jeff K.