When you attempt to join a Windows 2000 computer to a Windows NT 4.0 domain, you receive:

The following error occurred attempting to join the domain <DomainName>: The account is not authorized to login from this station.

You have probably set restrictive Local Group Policy, that is causing this, most likely in the
Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options path.

Set the policies back to their default value before joining a Windows NT 4.0 domain:

Digitally sign client communications (always) - disabled
Digitally sign server communications (always) - disabled
Digitally sign server communications (when possible) - disabled
LAN Manager Authentication Level set to Send LM and NTLM - use NTLMv2 session security if negotiated     - send LM & NTLM responses
Secure channel: Digitally encrypt or sign secure channel data (always) - disabled
Secure channel: Require strong (Windows 2000 or later) session key - disabled

Shutdown and restart before attempting to join the domain.