Backup your entire DC, including system state. Restore it in the test lab (that is completely isolated from your production network). Verify that AD is working in your test lab. Upgrade your schema from 2000 to 2003. Install a Windows 2008 R2 server in the test lab, join it to the domain in the test lab. Make it a DC, use it to upgrade your schema to 2008 or 2008 R2.
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CompTIA A+, Network+, Server+, Security+
MCTS:Windows 7
MCSE:Security 2003
MCITP:Server Administrator
MCITP:Enterprise Administrator
MCITP:Virtualization Administrator 2008 R2
Certified Quest vWorkspace Administrator