If you work as web designer or webmaster, you probably have every browser out there installed so you can see how your pages render for different people. Checking how it looks for different browsers, different resolutions, and even different devices is important to making sure your site is accessible to the largest audience possible. This is particularly a problem with Internet Explorer. Normally, Microsoft only allows you to have one version of IE installed at a time. You could upgrade from IE 6.5 to IE 7 and downgrade again to see how it looks in both of those browsers, but you can’t have them installed concurrently.
I previously found a way to do this that was a real hack-job of keeping IE 6.5 installed and inserting the needed DLLs for IE7 when starting up a batch script. It wasn’t very reliable and couldn’t really recommend it to people that weren’t willing to do extra coddling for the program.
Since then, I stumbled upon a much better way of doing it. A free installer from Tredosoft wraps it all up where you walk through the setup and check which versions of IE you want installed (3, 4, 5, 5.5, or 6). Shortcuts are created and you have reliable access to archaic versions of Internet Explorer. Plenty of people are still using these older versions, so it’s perfectly reasonable to test your site in these versions.
(direct link to download)