Running multiple versions of Internet Explorer side-by-side

I’ve written previously about using user agent spoofing to make Microsoft Internet Explorer (IE) 7 and Mozilla Firefox behave like legacy versions of IE but I just stumbled across this nifty method of running multiple versions of IE side-by-side. I haven’t tried it out yet and it’s unsupported by Microsoft but it sounds like an interesting idea for next time I’m doing some website development work.