This really boils down to your experience in dealing with Windows Server 2008. Most of you have probably dealt with DHCP, DNS, AD Administration and the usual suspects but how much have you looked under the cover of Server 2008?
The certification path you choose really depends on your experience. If you haven't touched 2008 at all, then you'll need spend a fair amount of time learning it, specifically the new Powershell commands and your way around the GUI. The GUI is always the thing that throws people when a new version comes out.
If you've been using Server 2003 for a few years, then go with the MCSE exams. You
should be able to get them done with just a bit of study time, then you can put
what you learnt into practicing on the machines you run.
Once you have achieved your MCSE, the upgrade path to Server 2008 is just a single exam for the MCTS, and another one for MCITP:Server Administrator. By the time you get to that stage, you should be looking to be in a job where they user Serve 2008 for all there own uses.
Its best if you try and achieve your exams in order so that you get your MCSA halfway through. Even if its not the certification you want to achieve, its nice to have a half way marker to work towards.
This is our recommended study path for MCSE:
70-270 or 70-620
70-290
70-291 – This one can be a really hard exam
Your elective choice (most commin is 70-284)
You have achieved the MCSA certification!
70-293
70-294
70-297 or 70-298
You have achieved the MCSE certification!