Here is an overview of what it takes to get the MCITP Certifications on Server 2008

MCITP: Server Administrator — Focuses on day-to-day operations and management

Exam 70-640 (earns MCTS: Windows Server 2008 Active Directory Configuration)

Exam 70-642 (earns MCTS: Windows Server 2008 Network Infrastructure Configuration)

Exam PRO: 70-646 (earns MCITP: Server Administrator)

MCITP: Enterprise Administrator — Validates your skills focused on Windows infrastructure design

Exam 70-640 (earns MCTS: Windows Server 2008 Active Directory Configuration)

Exam 70-642 (earns MCTS: Windows Server 2008 Network Infrastructure Configuration)

Exam 70-643 (earns MCTS: Windows Server 2008 Applications Infrastructure Configuration)

Exam 70-620 (earns MCTS: Windows Vista Configuration)
Exam PRO: 70-647(earns MCITP: Enterprise Administrator)

For upgrade from MCSA and MCSE the follow exams needs to be taken

Exam 70-648: TS: Upgrading Your MCSA on Windows Server 2003 to Windows Server 2008, Technology Specialist
Earns MCTS: Windows Server 2008 Active Directory, Configuration and MCTS: Windows Server 2008 Network Infrastructure Configuration

Exam 70-649: TS: Upgrading Your MCSE on Windows Server 2003 to Windows Server 2008, Technology Specialist
Earns MCTS: Windows Server 2008 Active Directory Configuration, MCTS: Windows Server 2008 Network Infrastructure Configuration and MCTS: Windows Server 2008 Applications Infrastructure Configuration

Visit the official Microsoft site for complete overview