Different versions of Internet Explorer are unable to run side-by-side on a single Windows machine without patching various files. Side effects have been reported with this method, and web developers often need to test their sites on multiple browsers and configurations. The official workaround suggested by Microsoft is to use Virtual PC to virtualise an environment with Internet Explorer 6 installed.
Today saw the announcement by the Internet Explorer development team of a free, downloadable, pre-activated Windows XP SP2 image with Internet Explorer 6 installed. Now that Virtual PC is also a free download, users no longer have to purchase an additional Windows XP license in order to test their sites in Virtual PC.
The image is time-bombed to expire in April 2007, but new versions (including images where Internet Explorer 5 is installed) are expected to be released.
Thanks to slimy for reporting this in Back Page News.