Domain Configuration

I have a small three location network I am migrating from Novell to Win 2000. Each location will have its own Win 2000 server. The main location will have the Exchange 2000 server loaded. The locations will be connected by T1’s. Current user connections not exceeding 50. What would be the most efficent structure for admin purposes with minimal line usage?

Can I setup three individual domains under the parent such as Main.mydomain.com, knox.mydomain.com and aave.mydomain.com or should I create the three servers under mydomain.com? I have setup numerous winnt and Exchange 5.5 this way but wonder what would be best for Win2000 and Exchange 2000.