Re-Entering Windows XP Product Key

When I was at church yesterday the pastor came up and asked me to look at one of the admin PCs - it was running slow and he asked me if I could install some more memory and clean up any spyware on the PC. So I went and installed the memory and cleaned off the small amount of spyware (tracking cookies, FunWeb) and went to the Windows Update site to ensure the latest downloads were installed. Windows wanted to validate the Product Key, only to find that it had been installed with a blocked Volume License Key and not the Product Key stuck to the side of the case. I also couldn't find a way to get the alternate validation method to work - the one where you get to enter a validation code and you just use the validation code from a system with a valid key.
A Google search (isn't Google just wonderful?) returned a site that provided me with a way to re-enter the key on the side of the case. Here's a rundown of the steps I took:

Run regedit
Browse to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\wpaevents
Modify OOBETimer Value
Change at least one digit of this value to deactivate Windows
Run cmd
cd %systemroot%\system32\oobe
msoobe.exe /a
Click Yes, I want to telephone a customer service representative to activate Windows, and then click Next
Click Change Product Key (at the bottom)
Enter the valid Product Key
Press Update and close the window.
Restart the PC

And voila! One PC with the blocked Volume License Key replaced with the valid Product Key that came with the PC. If only I'd looked for this info when I got my brand new laptop...