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Except that I don't think that helps those of us with licences from before v3.0. I've just upgraded to Leopard and have discovered the same...
I had made a back up on an external drive, it's in trying to use the backup that I have the problem. I'm not sure whether I really followed...
I've just had to replace the harddrive in my Macbook and have had to reload everything. XP installed and activated with no problems in Boot Camp...