I need to reinstall Win2k server

This article might help you: Microsoft Knowledge Base Article - 216993

in my opinion if your AD data base is damage, and you only have one server, you should backup the DIT, what on NT is called SAM and after you reinstall the new OS then you can use a backup Authoritative to resotre the old AD three ot DIT

Windows 2000 ships with a backup program that is Active Directory-aware. Go to start menu > run and then type ‘ntbackup’. Select the Backup tab to view a list of resources you can back up. Navigate through the list of resources, and you’ll see that beneath My Computer is a list of local drives and an object called System State. Active Directory, boot files and registry are the components included in the system state.

The restoration,
After you have reinstall the server, boot into Active Directory Restore Mode (Press the F8 when boot), logon using local administrator account and perform an authorative restore. When the restore completes, reboot the server. Windows will go through several steps to make the Active Directory consistent and will then boot normally. Do remember windows will prevent you from restoring system state data that’s older that older than 60 days.

Have a nice day! 8)

Don't do it, you might run into unexpected problems. Rather install Windows 2000 Server on another computer join the domain and run DCPROMO on the new Server, take over FSMO roles, run DCPROMO on the exisiting Server, reinstall. Run DCPROMO on the newly installed Server again, take over FSMO roles. Run DCPROMO on the second Server to make it into a member server. If you plan on running a backup on the computer you are reinstalling, run it after you ran DCPROMO on it. That way AD is not backed up.

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