How to merge 2 domains together

We have a customer who bought out another company and merged.

Right now we have both companies in the same building. they are both on different routers and different IP' ranges. and the other is

They both have their own domain controllers.

We are going to be bringing them on all the same network.

The company that was bought out uses a sql database program called Miracle.
all the client workstations have the Miracle executable and it is pointing to the database of the server using the Host name not the IP of the server.

Our question is is it possible to demote the server which is now a DC and add it to the main network at a child server?.

or can we just bring the server to the other network as a DC but turn off DHCP and DNS server?
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Brian BConnect With a Mentor EE Topic Advisor, Independant Technology ProfessionalCommented:
You can't merge domains, as in join the resources together. I suppose you could demote the old DC and then join it to the new domain, though I might suggest rebuilding it after you demote it, just to make sure the OS is clean.

You might want to read up on domain trusts though. I think that is what will work the best until you get everything moved over to the new domain.

As for the Miracle database, you can always manually add a DNS entry for it to the new DNS server.
Konstantin KrolikovConnect With a Mentor Commented:
You may do uplink between them and create forest trust. This will give users and resource trusts to interact on both networks.
About DNS you may configure secondary zone on both domain controllers of each others primaries zones.
At later point you can change UPN's for users like login with instead OLD-DOMAIN.

But as merge you will need to choose one of your forests to be primary for your self, leave old one and to join all resource, hosts to new domain.
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