These numbers might help:
http://www.thecounter.com/stats/2004/July/browser.php
TheCounter.com is a site used by literally millions. It saw over 200 million hits in July. People from all walks of life and all kinds of sites use them, so you see a very generous spectrum rather than a small focused group of users.
Internet Explorers 5 and 6 accounted for 93 percent of their traffic.
Mozilla products eked out a mere 2%, which is a shame because I use them every day and would like to have everyone in the office using them.
Ken's basically right on the money, even if he were to completely ignore the Mac market. Apple only controls roughly 6% of the world desktop market. Most casual users don't switch browsers, and since Macs come with Safari pre-installed it's probably not even a large base installed on Macs.
So you're looking at the majority of IE installs being on Windows machines, and that's still in the 90s percentage wise.