WHERE does it state that this server's role is a domain controller?
In Administrative Tools (either on your Start menu or in Control Panel), do you have any tools labeled Active Directory Users and Computers, Active Directory Sites and Services, or Active Directory Domains and Trusts? If not, how did you create user accounts for your "domain"?
Was Win2K SERVER installed from scratch or as an upgrade on an NT4 PDC?
The bottom line is that you CANNOT create a Win2K domain without implementing Active Directory. There is NO way to get around this.
Therefore, I suggest that you probably have a partial, though botched installation of Active Directory. Because it is a botched installation, you will not be able to add a second domain controller.
I suggest the installation is botched because you are using your ISPs DNS servers. Active Directory must add numerous records to DNS in order to work correctly. Almost ALL ISPs will NOT accept these records on their DNS servers.Therefore, is is pretty much mandatory to host DNS locally for AD.