Client cannot find domain

We have a WIN2000 server setup as Domain Controller running DNS and WINS. DNS is standard primary. AD is in mixed mode. The server has registered itself with both DNS and WINS. I can join a WIN2000 machine to the domain. I cannot join a NT 4.0 client to the domain. It reports it cannot locate the Domain Controller. The NT client has the correct WINS and DNS address for the DC. IT can ping and resolve the name of the DC. What am I missing here?