Lets back up a little it and see if we can clear up some of the confusion. As you know, in order to resolve names into addresses that can be routed, connectivity to a DNS server is required. The most common method of getting DNS access is from your ISP, who normally publishes a couple of public IP addresses for this purpose. Alternatively, you can run your own DNS server to perform the routing function. The most commonly used DNS server would be BIND, and Win Server undoubtedly has an equivalent. Every host on your system needs to know the address of an accessible DNS that they can query to perform look ups.
In a typical (e.g. residential or small office) configuration, the WAN (Internet side) configuration of a router is performed automatically and it acquires these addresses from the ISP. In some cases, the configuration is performed manually and these WAN side DNS servers are programmed in. Then when this router is used as a LAN DHCP, it passes these addresses to the hosts on the LAN. If the router is pointed to as the DNS, it would undoubtedly forward or relay the query to the ISP DNS servers.
What you appear to have done is change the DHCP server from being the router, which had obtained the DNS server information and instead used a server on your LAN. This is perfectly acceptable. However, in doing so, you did not configure it give out DNS server addresses.
Now, things can get a little bit complicated, for example, if you use DNS on your LAN too as your ISP is not going to have a clue about these addresses. In this case, your best option would be to use your server for DNS resolution and point your LAN hosts at it. In this case, your ISP's DNS entries should go into the forwarders section, which means that if your LAN DNS can not resolve the query, it will check with your ISP's servers.
