Question : Merging Windows 2003 Domains in same Forest

We currently have 7 domains. The root domain is company.com and the child domains are x.company.com, y.company.com, etc... We have an Exchange 2007 server that is located in the root domain and file/print servers that are located throughout the child domains. What would be the simplest way to merge all the domains into the root domain?

Answer : Merging Windows 2003 Domains in same Forest

You're probably going to have to migrate all the resources from the child domain in to the root domain, and then demote each DC in the child domains until all the child domains are gone.

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