Here is a quick road map on 2008 certs.

Upgrading from MCSE you will want to get to you local testing canter and write Exam 70-649: TS: Upgrading Your MCSE on Windows Server 2003 to Windows Server 2008, Technology Specialist. This will let you pass the 3 major Technical Specialist exams in one shot.

70-640: TS: Windows Server 2008 Active Directory, Configuring

70-642: TS: Windows Server 2008 Network Infrastructure, Configuring

70-643: TS: Windows Server 2008 Applications, Configuring

Once that is out of the way you can complete Exam 70-647: Pro: Windows Server 2008, Enterprise Administrator which certifies you as a Microsoft Certified IT professional (MCITP). In order to get the MCITP though you'll also have to certify on Vista either 70-620 or 70-624 will be sufficient.

If your coming from MCSA you'll want to look at Exam 70-648: TS: Upgrading Your MCSA on Windows Server 2003 to Windows Server 2008, Technology Specialist This covers 2 TS exams.

70-640: TS: Windows Server 2008 Active Directory, Configuring

70-642: TS: Windows Server 2008 Network Infrastructure, Configuring

The next exam is Exam 70-646: Pro: Windows Server 2008, Server Administrator Which again gives you a MCITP but the focus is more on servers as apposed to larger enterprises issues.