Here is a big tip for web developers and anyone else that is involved with email rendering and testing.
Imagine testing with legacy versions of IE (4, 5, 6) for rendering with your email or your landing pages, having to reconfigure your system each time to have the proper browser installed (because you can only have one installed at a time). Well say good by to virtual machines, or managing separate systems to view all of these different versions. The people at this site looked at the code behind the browsers and made them work independently from the Operating System. Without reinstalling your systems core browser you can run IE7 and IE 6 and IE 5 all at the same time!