By adding a new domain controller to the domain the Active Directory Schema (users, groups, login scripts, etc) will get replicated. Any files and shared folders will need to be copied manually. When you run dcpromo to demote the old server then everything will function using the new DC.
If you want to transfer the FSMO roles by hand before demoting the old server this article explains how to do that:
http://support.microsoft.com/default.aspx/kb/255690Dave