Yep, absolutely could be. What you would need to do is completely remove that server from hosting DNS. You don't want this server to run any DNS service at this point. If that server is still a domain controller, you'd need to DCPROMO it as well to make it just a standard server. Then in the TCP/IP settings of the Local Area Connection, just point DNS to the 2003 server and ONLY that server. Do not use any other DNS servers at this point.