[link|http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038&DisplayLang=en|http://www.microsoft...38&DisplayLang=en]

It's an imitation of the Web Developer extension for Firefox. Decent, as far as Microsoft "innovation" goes, but it seems to be lacking the important feature of editing CSS on the fly.