Why only install IE6 and 7 when you can be like me and make yourself want to jump off a bridge sometimes.
I have damb near every browser I know of installed, now I only need to buy a mac and get any damb browser the macs have, I do this so I can easily cross reference my webpages when checking out browser compatibility, but by having too many browsers for testing your sites it gets frustrating because one thing will work on two browsers and not on the rest so you change it to suit the other browsers, then the ones that were good are no longer good, can be a real nightmare sometimes.