DNS & AD HELP

I think i need help
I have one existing Windows 2003 server running DNS & AD in the office and 5 pc?s with w2k all working as a domain.
But the boss has a new w2k server in his house, and would like me to set it up to join the domain and run AD on it. As a backup for the Data Base.
Do I need to setup VPN first ?
I have a Domain Name setup (clevedondomestics.org) and it points to the office IP.
But when i try to add the new server from the bosses house to the office domain i keep getting error DNS name does not exist.
Any Help & where do i start.
Thanks
Paul