Windows 2003 Domain Controller

I have a windows 2003 domain mydomain.local with active directory installed. I need to setup a standalone server that would host my public dns, exchange and iis6. My public name server (NS) is dns1.mydomain.com. Can this stand alone server join domain mydomain.local or I have to convert the standalone server to a domain controller mydomain.com. I need my dns server respond to (soa record) dns1.mydomain.com.