This one's Expression, which is a vector-based draw program similar to Adobe Illustrator and the like. For a long time it was a commercial product offered by Creature House and was licensed by Metacreations back when they were an industry player. Creature House was also working on an animation plug-in that was based on their vector graphics engine, which is why Microsoft got interested in 'em. After the MS buyout, Expression was unavailable for purchase and had a future that was in doubt, as Microsoft was interested in the underlying technology and not the tool.
A ray of hope showed up about a month ago when MS released the OSX version of Expression for download, and now they've done the same with Windows. It advertises itself as a 'preview' release for existing Expression customers, but doesn't have any eligibility requirements that I can see. Only problem is that it's a 57 meg download, which will be a problem for you dialup types.
If you're in need of a vector-based draw program, this is the one. I tried its 'export in Flash format' function, and it imported into Flash flawlessly, which'll make it a nice add-on for Flash developers such as myself, as it appears to be much less complex than Illustrator. It's also got the ability to create Flash buttons directly, which is nice.
Looking at their Expression discussion forum, it appears that there's not yet an official company line as to where Expression is going. The product manager did mention that the only change between the Creature House version and the Microsoft version is the licensing agreement, so I don't think there are any content limitations or timeouts or anything like that. If the Creature House engine becomes something used at MS, Expression will likely live on as a content creation tool.
Until then, happy drawing. Be sure to check out the sample drawings. If you haven't used a vector drawing tool in a while, you'll be amazed at the stuff you can make with it.