Great news, I just found a simple software that installs multiple IE's on your Windows machine.
I think this solution is great, at least much better than Microsoft's native solution to have VPC (Virtual PC) and run each version of IE in it's own environment. Believe me, you don't even want to know.
Instead, this software installs older versions of IE on your machine, assuming that you're running latest version (IE7+) as your default browser. You can then run and test your web site design in each version independently.
ATTENTION: It may not work on Windows Vista. Please read the author's web site first.

