Since the arrival of IE7 there have been a number of workarounds developed to enable designers & developers to test their site in IE6 & IE7 on the same machine. However, none of these have been entirely successful; for example the standalone version of IE6 I had installed didn’t work with HTMLconditional comments, so my IE6 style sheet was not picked up.
Now MS have come to the rescue with a free virtual PC installation that allows you to run IE6 on your machine. It’s essentially like running another version of windows XP on your PC simultaneously.
The virtual PC image is time bombed, so it won’t work after April next year, but by then hopefuly IE7 will be ubiquitous and we can forget IE6 ever happened.