Gabe Knuth has wrote a very good article about Microsoft's Desktop Virtualization product line as of 2009

Last up in our rundown of the Big 5's desktop virtualization product lines is Microsoft.  This is probably the most ambiguous vendor, because so many of their products intertwine to make up their solution.  Many of those products have been around for a very long time, and in other capacities, so it's not easy to pick which products to focus on.  To make it easier, this article will only cover the products listed on Microsoft's Virtualization Products and Technologies website. (http://www.microsoft.com/virtualization/en/us/products-server.aspx)

Check it out there