Have IE6 and IE7 installed simultaneously

This is a very helpful thing if you need to do browser testing on version 6 and 7 of IE from the same computer (and you don't want to have to run a virtual machine/virtual PC instance):

Install multiple versions of IE on your PC

I installed it on Win XP pro and it works perfectly (and IE7 still works too!)

For the record, I only use IE for testing. Firefox 3.0 is my main browser.