Does Microsoft support any method for transferring an Exchange 2000 Server system from one domain to another?

No, Microsoft doesn't support any method for migrating an Exchange 2000 server from one domain to another. If such a migration is crucial, your best bet is to set up a new server in the target domain and move the source server's mailboxes and public folder replicas to it. Alternatively, you can attempt a disaster-recovery—style transfer, in which you perform an online backup and restore it to a machine with the same name in a different domain. However, this approach requires, at a minimum, that you use the /disasterrecovery switch to install Exchange on the new box and might require you to use ADSI Edit to adjust the distinguished name (DN) of various server objects, as Microsoft's Exchange disaster-recovery white papers describe.