I didn't use the keychanger; instead I followed the instructions above step by step and everything worked as described;
I did make sure that I used one key generated by
and I also made sure it'd be appropriate for the CD I have; I discovered that not all keys are accepted and I tried them until I found one that was accepted by the CD. In order to do this just pretend you're installing XP until you're asked for a key and see if it's accepted. One may have to try several until a suitable one is found; I had to try more than 20 to find a good one.
I also went here
to make sure I had the new key activated before running SP1.
Afterwards I just applied SP1 and I had no problems at all.