A while back, I found a multi-IE application which can run IE versions 4-6 and since I had to test a site in IE6, it worked great.
The only problem was, it killed my IE7 installation; so I tried to install a standalone IE7, but it had a few problems that kept it from being useful at all. So with a bit of research, I found an application that is currently supported that runs IE from version 1 (why would you want to run IE1?) all the way to IE8 - it lets you choose which versions you want installed.
So I have deleted 2 of my Windows VM's and I now only have 1 VM that runs IE8, IE7 and IE6 (saved myself 20GB of disk space
and so far, IE6, IE7 and IE8 seem to be working great - except if I have all 3 open, my user agent shows up as IE6
Without further ado, here's the link: http://finalbuilds.edskes.net/iecollection.htm
P.S. They also have a link on there for a silent FireFox installer - which you could make it automatically download and install FireFox on your system
nice trick for your users who are still running IE6
I also found a couple of great debugging tools that give you about 90% of what FireBug gives you in FireFox - I'll post those in another topic later on.