This is one of those people who go on and on without knowing what he's really trying to do.

Windows 2000 has "Internet Connection Sharing" and that will use whatever DNS entries the external card uses, assuming he set up in compatibility mode. If he set up in "pure AD" mode as a domain controller then he has to have a local dynamic DNS server going, so again there is no issue. If he doesn't want to use ICS then he had to get a third party NAT program like Winroute (which can also do DHCP and forward DNS queries).