Thanks Warp2search for the heads up on this story. The Change your Windows XP product licensing key - Microsoft shows you how story still receives a lot of hits, despite being over a month old.
Seems many folk may find the instructions Microsoft published for changing the key useful.
One guy who did seem to have found it useful is INQ reader Ryan. Yet he decided the operation was a little too cumbersome, so he wrote a little routine to automate the process, which he posted here.
Ryan reckons this is the only tool available perform the operation. We haven"t tested it (why should we need to?). Let us know how it stands up.