W2K3

I have an NTs4 PDC , no BDC. I have a new HP server with Win2003 SBS premium. I want to add it as a domain controller, and later use my NTs4 as another member server (demote), and not decommission it. As I am loading the DNS name in the W2K3 and the Netbios domain name, it says, " being used already or already exists" , obviusly, it exists, but how should I go about it loading in my domain. At the moment the WIN2003 is in a Workgroup. but before I can migrate, I have to get pass this initial error. I don't want to use another domain name. DO you recommend I use ADMT at this stage? I am not doing a domain upgrade, but a domain restructure. Im currently reading, migrating from WindowsNT4 to SBS 2003 from Microsoft, but It does not cover what I am experiencing right now.