This is an extremely important issue and I always pay special attention to it.
I have Internet Explorer 7, which you can download from Microsoft website for free here:
http://www.microsoft.com/windows/dow.../getitnow.mspx
I have Internet Explorer 6, which you have to download the Standalone version so it can run with IE7 from here:
http://browsers.evolt.org/download.p...e6eolas_nt.zip
FireFox from here:
http://www.mozilla.com/en-US/firefox/all.html
Opera from here:
http://www.opera.com/download/
And finally Safari, which is now available for Windows from here:
http://www.apple.com/safari/download/
PHIEW
It might sound a little too much, but when I'm making a web page I have all my different browsers open and pointing to it, and I make sure my web page looks the same on all of them.
From my experience, a little bit more than 50% of visitors use IE7 and IE6, the other 50% are using all the other browsers I mentioned here.
The days that Internet Explorer shared most of the browser market are over and even if it wasn't, I would do the same.
I also don't think anyone wants his/her website to look broken on say 10% of their user's browsers, and this is the only way to test it and be sure.
At first it's a little hard to get used to making a web page this way (it means extra work, of course), but when you get used to it (which happens very fast

) then there is no way that you'll want to make a web page any other way