it's lovely that you guys want to argue about browsers and what not, but when it comes down to it, a HUGE percentage of the market still uses internet explorer, because that's what their computer comes with. you can say it sucks, but that's how it is.
i think that the operating system you do the coding on is highly irrelivent, and you can get almost every browser for most systems, except, unfortunetely, Internet Explorer. So IMO, the best way to go about this is too design the site using which ever OS you prefer, then when you're finished, test and trouble shoot on as many browsers as you can to make sure they all look the same.
the top ones you want to check are:
Internet Explorer 7
Internet Explorer 6 (definitely make sure you check it on 6, there is a lot of bugs in 6 that trip up a lot of coders and i believe this is still VERY widely used because of Windows XP)
Safari
Firefox (if possible, for right now, i would try and test under v2, and v3)
and Opera
EDIT:
side note* this is only my own list for what i believe are the top browsers in the world, if you can test more definitely do, and try and keep up to date on the most popular browsers and always make sure to test your sites on them.