You should only need ONE domain in Windows 2000. You don't mention NT4 or previous versions, so I don't see any requirement for you to run a pdc. In Windows 2000, there is no PDC or BDC (only a PDC emulator). Instead you can have multiple domain controllers (or only one if you choose) with some or only one performing specific master roles and member servers. The first domain controller installed in a domain is automatically assigned all the operations master roles. You can change the assignment of operations master roles after Setup, but in most cases this will not be necessary. I would recommend one domain controller with the 2nd system that you want your data on configured as a member server and an application or file server for shared access across the domain. It wouldn't be a bad idea for this server to be a domain controller also (but not performing any master roles) to allow replication of active directory. I recommend you read up on this before you continue by checking out the following link:

http://www.microsoft.com/windows2000/en/server/help/