Is is possible to take a BDC from Domain A, change it to Domain B and then promote it to make a PDC on Domain B. If this is possbible, would there be any conflicts with Domain A once it is up and running as Domain B? What I am wanting to do is make a test domain with the exact accounts from my production domain. Thanks, Scott

Yes you can do as you have outlined but the two servers can not be on the same wire. In other words no communication between the production network and test network.

Why is that? Is it a SID issue? If I change the SID with NewSID from sysinternals, would that make it possible to put them on the same wire?

Yes you are right. It is the sid. But it is also the domain name. After all you want this as a pdc of the same domain name. You can NOT have two PDCs of the same domain name on the same wire. The whole point of a test lab is that its isolated from the live network. This way you can test things without impacting the live network. You are going to need a workstation in this lab. Now perhaps you have a shortage of hardware and want to use the same switch for both domains. You would need to configure the test lab domain to use a different subnet than the live domain. Due to this ip difference they will not communicate with each other. Or if you have a managed switch you can use vlans to segment the network physically and not change anything on the lab server.