Don't understand the differences in these Microsoft certs

I know some about the MCSA/MCSE for Windows 2003, but how do they differ from the MCTS/MCITP on Windows 2008? Is it an update/upgrade cert or something altogether different? I wouldn't want to study for an older cert when I should be going after the newer one. Thanks.
Comments
The MCSA and MCSE certifications are comprised of administration and design exams. Some focus on administrating, managing, and troubleshooting a particular aspect of a Windows 2003 network, while others focused on the design and scalability of those various pieces.
The MCITP: Server and MCITP: Enterprise certifications have two parts as well, but they differ in the approach. There are several Technology Specialist exams for each, which focus entirely on making you adept with the particular feature(s) and functions of the software and tools. The PRO exams are like the design exams on the 2003 track, but focus much more the business of managing a Windows 2008 network in respect to design, administration, and security than the older design-focused exams did.
For all intents and purposes, MCITP: Server Administrator is to Windows Server 2008 what the MCSA is to Windows Server 2003 and MCITP: Enterprise Administrator more closely reflects the skills measured by the MCSE. It's not an exact comparison between the respective certs, but it's close enough that most people will see it that way. If you're working with the 2003 technologies, go for the MCSA/MCSE track and possibly upgrade in the future. If you're working with 2008, go for one of the two MCITP certs.
Another point of confusion for people is that Microsoft calls each professional-level certification they release for each of their products MCITP. You can become MCITP certified on Exchange 2007, SQL Server 2005 and 2008, Project Server 2007, etc. You can find a full list here.
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The MCTS or Microsoft Certified Technolgy Specialist is much closer to the MCP designation with a slight difference. The MCP requires only one exam. The MCTS may require more than one exam to qualify. The MCTS exams are, as the name implies, designed to show expertise in a specific Microsoft technology. It may be Vista, SQL, 2008 Server, or a variety of other specialties.
The MCTS and MCITP are newer certifications for the newer technologies but this doesn't mean you should rule out the older certs. The older certs cover technologies that are still very much in use and will most likely be for quite some time. The MCSE may be more attractive to a company that is still using 2003 Servers with no need to upgrade in the foreseable future. The MCITP cert may have little use for them. Human Resource departments may not even recognize what they are yet.
I am sure that the newer certs will have a longer life span but you need to choose the path that works best for your circumstance. For me, I have experience with 2003 Servers. My company is starting to add 2008 Servers but they are no where near the majority or even common yet. I will take the MCSA/E track for now and take the upgrade test later when it is more in demand in my company. That matches with my circumstances. Yours may vary.
Good luck whatever you decide. I hope this clears things up and helps you make a good choice for you.