Run multiple versions of Internet Explorer on Windows

Windows has always been a bit of a pain when it comes to Internet Explorer versions: it only allows you to have one installed. This makes testing problematic: it means, for instance, that I have to have several Windows XP installations in Parallels Desktop and load them up when needed. However, there now seems to be a solution:

Run IE5, IE6, and IE7 at the Same Time - Even On a Mac

Just three installs and you are done! IE3, 4, 5, 5.5, 6 and 7 on one copy of Windows! Lovely!