Watchgaurd x700 and Win2K DNS

I have a Watchguard x700 firewall and it has a trusted port and a DMZ port. The websites are on the optional (DMZ) port. The websites can be viewed from the outside (www.crestpt.com) but not inside. Watchguard says I have to setup my DNS server for that. So how do I do this. Make a FQDN name go to 10.0.0.5?