On your Windows 2003 machine, run DCPROMO & follow through the wizard to create your domain, advising it that this is a NEW domain.
If you have a second 2003 machine, 1/2 hr after the 1st one has completed it's promotion ( lots of processes still run in the background after the wizard stops ), run DCPROMO again & this time select to join an existing domain.
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Now you have a domain.
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Got to each of your client workstations ( cannot be home edition as this doesn't support connection to an AD network ) & right click My Computer. Select properties.
Inside the properties box, select computer name tab.
Click the radio button & enter the domain name managed by your DC (s).
Once you click OK, it'll ask for account details within the AD domain with rights to add the machine into AD. Enter this, click enter & hey presto.