If you need to add a further domain controller to an existing domain/Forest you can consider these articles about this procedure.
https://technet.microsoft.com/en-us/library/cc753720(v=ws.10).aspx
http://www.rackspace.com/knowledge_center/article/installing-active-directory-domain-services-on-windows-server-2008-r2-enterprise-64-bit
This is relative article that I follow during this years about 2008 R2 server
http://kpytko.pl/active-directory-domain-services/adding-additional-domain-controller/
