RedManBlueState

I need help with what should be an easy DNS question. My customer owns a domain, lets call it "domain.com" which is registered with his host's DNS as SOA. I configured a new AD forest in his office and called it internal.domain.com. AD DNS seems to think it is authoritative for domain.com, and won't resolve the external hostnames (http://www.domain.com, ftp.domain.com) Shouldn't Windows DNS authority end at internal.domain.com and automatically pass domain.com to root servers?