Question : How to make a single domain controller/dns box an authoritative dns box

when I try

Using Nslookup
From your DNS server, type nslookup at a command prompt.
Type set type=all, and then press ENTER.
Type _ldap._tcp.dc._msdcs.domainname (where domainname is the name of your domain), and then press ENTER.

I get the retort that

_ldap._tcp.dc._msdcs.domainname : non-existent domain

DNS is my weakest area.

Answer : How to make a single domain controller/dns box an authoritative dns box

I suppose your client has the DNS value key in their TCP/IP properties. Or are u using DHCP ? And are ur clients and DNS in the same Domain ?