If there's one thing we all agree on, it's the collective joy we feel when testing for multiple versions of Internet Explorer. Okay -- just joking -- but any tool that makes that task a little easier has to be a good thing, right?
In the last 12 months we've seen a few applications that attempt to streamline the testing process, perhaps most notably IETester from My DebugBar. Now Microsoft themselves have come to the party with Expression Web SuperPreview for Internet Explorer. First impressions are fairly good. Like IETester, SuperPreview allows you to simultaneously load two IE renders into the same application view.

Some quick points worth noting:

• These are live renders, rather than screen captures, and the application allows you to select and interact with the DOM in a Firebug-like way.
• You're free to pan and scale each browser window.
• SuperPreview gives you a nifty Overlay Mode, which allows you to compare subtle positioning differences between browser versions.
• By default, SuperPreview allows you to test in IE8, IE in compatibility mode (that is, IE8 pretending to be IE7), and IE6.
• Although SuperPreview currently only supports Internet Explorer, the release notes point to support of other browsers in the future. But I'm unsure if that's a good idea.

On the Downside ...
There are a few aspects of SuperPreview that need some work, in my opinion. Performance was an issue on my system with everything slowing to a crawl while SuperPreview was open. It also seems to lack IE5 testing ability, although perhaps the relevance of testing for that browser is questionable in 2009.
Of course, this is a beta, so there's a good chance at least that the performance issues will be ironed out by release time.

More worrying is the assertion in the release notes that "Pages previewed in Internet Explorer 6 may not display with complete accuracy." Okay, so what exactly is the point here?

For what it's worth, my comparisons of a stand-alone IE6 install and the SuperPreview version seemed identical. Hopefully they're just being overly cautious.
Whether they intend to charge for SuperPreview is unclear. You would hope that a tool designed to help developers give IE users a better user experience would be free. We'll see.

Assuming Microsoft are able to work through most of those issues before the release, SuperPreview for Internet Explorer might be a handy addition to your testing process.