It appears Microsoft is making web design testing a lot easier (or at least taking some time out by removing the need for VirtualPCs with different versions of IE on) with a FREE application called Microsoft SuperPreview.
With a large number of people still using Internet Explorer 6, this is nothing but a good thing until IE6 is gone for good.
SuperPreview is available for download in beta from Microsoft. The download weighs in at 250MB and requires .NET.
For more information on SuperPreview see the article on Sitepoint called Microsoft SuperPreview: a New Way to Test Websites.
Also check out IETester which is also free.