Question : How do I add DNS and subdomains withing AD?

I wonder if anyone can offer a solution to my problem? This is the scenario: My old company  (Mycompany1.com)has been taken over by another (NewCompany1.com).  The new company is a larger concern mainly based in Europe with no Domain structure  they plan to go over to AD  in May/June. MyCompany1 has an AD structure and Exchange mail etc. The old company domain name cannot be used legally after end of March so we have bought a new domain name (NewDomainname.com) approved by NewCompany1 which will eventually become a trusted domain within the AD Forest when the new company set it up.
However, there are some factors that are causing me some concern.
We currently have several sub-domain names that allow external  http /https connectivity to Sharepoint, a development software package and other development boxes  thats not a problem as these can be re-configured and new subdomains can be pointed at our current IP address through DNS manager with our service  provider.

The parent company will be installing Exchange server 2007 in Europe and it looks likely that our Exchange  server may be used or completely decommissioned  who knows&  so far creating NewDomainname.com from scratch is a good idea as its name has some similarity to the new companys existing domain name and we can add this as a trusted domain to theirs later.
The problem; Im only really an basic  AD admin and havent set anything like this up before and would be grateful for some technical advice and  pointers on how to achieve;

a)      Create a child domain to the existing domain (MyCompany1.com) and its pros/cons.
b)      Renaming AD to the new domain name from scratch (NewCompany1.com) -  timescales, difficulty..etc
c)      Is it possible to use both the old and new domain names to both point to the existing servers (ie. MyCompany1.com and newdomainname.com use the same IP addresses to each server) , or will this end up resolving incorrectly ?

What has been done already:   I have set up the new domain name and subdomains to point at the existing servers that require external access (extranet, sharepoint etc).  Nothing has been done to the old DNS settings with the old service provider as the new DNS hasnt come on line yet.

Thanks, in advance.

Answer : How do I add DNS and subdomains withing AD?

The migration is fairly easy on you in that respect. There are a few instances where risk is high, but that will be limited to what happens when you move a single host or account rather than it being capable of knocking off the entire domain / forest. In short, you can control the risk.

If you're going down the migration road you'll want to start having a play with ADMT (Active Directory Migration Tool). The documentation is long, but it will do pretty much everything for you (copying accounts, moving computers, translating permissions, etc):

The program:

http://www.microsoft.com/Downloads/details.aspx?FamilyID=6f86937b-533a-466d-a8e8-aff85ad3d212&displaylang=en

The guides:

http://www.microsoft.com/Downloads/details.aspx?familyid=D99EF770-3BBB-4B9E-A8BC-01E9F7EF7342&displaylang=en

http://www.microsoft.com/Downloads/details.aspx?familyid=6D710919-1BA5-41CA-B2F3-C11BCB4857AF&displaylang=en

And for copying passwords when you migrate the users:

http://www.microsoft.com/Downloads/details.aspx?familyid=F0D03C3C-4757-40FD-8306-68079BA9C773&displaylang=en

As I say, there's a lot there. However, once you get into it it's no where near as bad as it looks at the outset.

Chris