There's really no way round it. However unfortunately, the vast majority of web users use IE6 on XP and it doesn't render code like anything else. Either you need to buy a PC (any old piece of second-hand crap will do, shouldn't cost tooo much) or get Virtual PC.
By sticking to validated Strict HTML4 and CSS i can get my sites to render perfectly in Firefox and Safari, sometimes a little odd in Opera, and, with a bit of "breakage", in IE6. I've given up trying to get anything sensible to work in either Netscape 4.7 or MacIE5 (which has to be the doggiest of dog browsers and unfortunately the only one available to our design studio who are still stuck in OS9)
IE6 has completely non-sensical ways of interpreting floats, margins and padding which i've never got my head around, and only managed to get working by endless "try this and see" methods. You really need a copy of it to test your pages in.