I thought it was like 97% Windows, 2% Mac, and 1% "other" where *nix, BSD, and whatnot fit that last 1%
In so far as the consumer market, Microsoft
IS the market. I'm sure the business enviornment might be a little different; Microsoft probably has near fifty percent as well, but nowhere near the domination of the consumer segment
edit:
similar to drag
edit:
though in academia Apple has a huge following...so many of my friends and faculty have Macs...specifically the laptops. The most common PC laptop I see are the IBM T series...With faculty I wouldn't hesitate to say atleast sixty percent have Macs