You want to rename a domain controller.
126.96.36.199 Windows 2000 Active Directory
To rename a domain controller, you must first demote it to a member server. You can then rename it and then promote it back to a domain controller.
188.8.131.52 Windows Server 2003 Active Directory
> netdom computername <CurrentName> /Add:<NewName> > netdom computername <CurrentName> /MakePrimary:<NewName>
There is no supported means to rename a Windows 2000 domain controller in place. That is why you have to fake it by demoting the server before doing the rename. Before you demote the server, you should transfer any FSMO roles. Alternatively, you can let dcpromo transfer the roles during demotion, but you should check afterwards to verify which server(s) the role(s) were transferred to. Likewise if the domain controller is a global catalog server, ensure another global catalog server is available to cover for it.
Renaming a domain controller is a new feature of Windows Server 2003. A new option has been added to the netdom utility to allow an alternate computer name to be associated with a computer in Active Directory. Once you've added a new name, you can then set that name to be the primary name, thereby renaming the computer. The old name effectively remains with the domain controller until you remove it, which can be done using the netdom computername /Remove:<Name> command. You should reboot the server before removing the old name. The old names are stored in the msDS-AdditionalDnsHostName and msDS-AdditionalSamAccountName attributes on the domain controller's computer object.
3.7.4 See Also
MS KB 195242 (Cannot Change Computer Name of a Domain Controller), MS KB 296592 (How to Rename a Windows 2000 Domain Controller), and MS KB 814589 (HOW TO: Rename a Windows 2003 Domain Controller)