2 Domains and 2 Exchange server in 1 IP subnet

[Dehcbad25]

I need some help. I am trying to find the best way. Even though I have a lot of ideas, I don't have a clear path, and since I lack technical people to bounce my ideas into, I will bounce them to TZ
The company I work for re-opened under new management. The new management has already a domain controller with Exchange on it (in the same server and it is not a SMB). Lets call this DomainB
My network has 2 domain controllers and a separate exchange. Lets call my network DomainA.
I think that the best solution is to put DomianB inside DomainA servers and demote the server that is currently hosting DomainB since it has also Exchange. As for Exchange, I also think that the Exchange server from DomainA is more beefed up and should absorb DomainB exchange.
DomainB only has 7 users, so at most it has 10 accounts, while DomainA has 120 accounts. I am even considering not having DomainB at all, just have Exchange being able to send and receive email from both domains.
If there are documents about how to approach this or any tips it will be helpful. Honestly I had such a crazy week I had no time to check MS web site yet, and I am sure it is full of useful information. With luck some other fellow TZ memer has a nice suggestion or tip to easy my craziness :p

[Curio]

As I am sure you are aware Exchange can handle multiple mail domains and you can set each users default mail address within Active Directory Users and Computers. You can set the exchange servers to talk to and through each other if you want to keep both exchange servers. With domain B having so few users it must be fairly easy to migrate them to domain A and maybe integrate the server as a member server with/without exchange as part of domain A. This looks to be pretty much the way you were thinking anyway,

[Dehcbad25]

Yes. To be precise, so far my idea is to just create a domain in my domain controller for the other company, and create the users manually (since they are only 7), and for the exchange I am thinking of using exmerge to export the email to PST, create their accounts in the new domain using my exchange server, and import the email using exmerge again. Then change the mx record for the domainB to point to my exchange server.
I am trying to avoid using their server since it has Windows Server 2003 standard, with both AD and Exchange on the same box. A setup that I do not recommend/like
After doing this, I just need to copy the shared folders that they have on the server which are not very big, and that is it.