Domain controllers are all at the same level.
Win 2000 also lets you upgrade to a domain controller and demote to a member server without too much of a headache. Just run dcpromo from the Run menu, and the active directory wizard will start. I do not know much about your situation, but I would not want to have multiple domains in Win 2000. Unless you have a good reason to use multiple domains, I would stick to one. You stated that under W2K just one domain is better.