humm, I'll assume that you have W2K server with DNS, AD, DHCP etc [makes it a DC] installed on it. I'll also assume that you configured your server with a static IP address . Now to reach the internet, you probably has to specify a default gateway and DNS server on the W2K server. In setting the DNS server on the NIC, you should have both your W2K Server IP address AND your ISP DNS address, preferably your W2K server box 1st and your ISPs DNS's second [plus populating a list of additional DNS servers in the TCP/IP advance properties DNS page. Also you need to enable fowarders on your DNS server. That way unresolved queries to your DNS server will be fowarded to your ISPs DNS server [or root name servers on the internet].
You could probably not go through all this and just multihome your W2K box. That way theres not confusion.