I often get asked about the changes to the certification roadmap for Windows 2008, but I have never had the time to go find the answer out as it did not seem straightforward.  So, I always said to the person asking that they should go see http://www.microsoft.com/certification as it is all explained there.  Well, thankfully, someone else has blogged about this with the answer!  Go see it here:

http://blogs.technet.com/james/archive/2008/01/21/windows-server-2008-certifications.aspx