I will open Active Directory Users & Computers and copy the Administrator Account creating a User, SOE for installing Workstations. I then add SOE in the GPO to allow that account to Add Workstations to the Domain. Then I will go to a workstation and logon as the Local Administrator, in Control Panel, select the Network Connections, Local Area Connection, right click and select Properties, select Internet Protocol and Properties, Tick Obtain an IP address automatically and the same for Obtain DNS server address automatically. In Control Panel, select the System icon: Select the tab : "Computer Name" To rename this computer or join a domain click change Type in your Domain Name a box will appear asking for a Username and Password Type in a username and password that has permission to add a PC to the Domain.
All going well you will have a proper connection.
I haven't yet had to create a Computer Account to add Workstations to a 2003 Domain. The Account will be automatically created. Anyone with a Domain Account will be able to logon to the Domain.
If you have cloned these PC's from an Image there is a good chance that they have an identical Computer Security Identifier (SID).
I normally run newsid.exe on each PC to create another SID.
http://technet.microsoft.com/en-us/sysinternals/bb897418.aspx
http://technet2.microsoft.com/windowsserver/en/library/7207aa3e-d95d-4176-a1ca-bc629f1ca6981033.mspx?mfr=true