On this website, you can run a browser based “virtual machine” which loads IE 6/7/8, Firefox 2/3, Opera and Safari (all for Windows). Only problem: Requires Windows and IE to run. But still: quite handy if you don’t want to mess around with your installation of win/IE (in my case, the VM running on OSX :P) but still want to be able to view your websites in different browsers and be actually able to browse them.