You don’t need to put the IP of the ISP DNS server any where. The DNS Server on the domain controller will already know the IP addresses of the Internet root DNS servers which it will use to find the web sites on the internet.
Make sure to install the DNS service on the domain controller before making it a domain controller, and put the IP of the domain controller before making the machine a domain controller.
Check out Michael Khanin’s blog on Windows and Network Administration.
added 12/31/07 by spadasoe:
You can include your ISP DNS by adding them to your DNS configuration on the forwarders tab of your DNS properties.