A Spoon That Tests Your Web Site
This is just a quick recommendation: I recently discovered Spoon’s browser sandbox, which allows you to test a site against any browser. This way, you don’t have to keep your own virtual machine with XP just to test your web-app with IE6. I also found it useful when browsing older web sites that don’t support my choice of browser. Spoon does require you to install a plug-in in your PC, but after that it worked flawlessly for me.