No it will not be possible in Windows 2000 without rebuilding the domain.
You can perform domain renames in Windows 2003. It one of the new Active
Directory features.
There is a workaround that will allow you to rename the DNS domain name by
introducing a NT BDC into the domain but I do not believe that this option
would work for you since you are using Exchange 2000. The steps are listed
in the article below
292541 How to Rename the DNS Name of a Windows 2000 Domain
http://support.microsoft.com/?id=292541
--
Tim Hines, MCSE, MCSA
Windows 2000 Directory Services
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