Windows XP overtakes Mac

There are probably now more Windows XP users than Mac users, but it is hard to say because there don't seem to be any reliable figures. Microsoft has now shipped 46 million copies of Windows XP, and if "product activation" works, this should be about the right number. (If not, the installed base could be 90 million or whatever.) But how many Mac users are there? As far as I can discover, Apple has been pretty quiet since 1997, when it claimed an installed base of 21.8 million. Given the decline in Apple's sales since then, it doesn't seem too ungenerous to imagine that it could have doubled its installed base. If so, it's already behind. If not, it may take another month or two....