Making Additional DC and Moving FSMO Roles

From The Domain which want to make additional one,

Run DCPROMO from your server and select “additional domain controller for an existing domain” option. This will add additional DC in the same domain.

If you have FSMO roles on DC1, move those roles to DC2 or DC3 before you retire DC1. You can identify the FSMO role details using the following command:

Netdom Query FSMO

Here is the procedure to move FMSO Roles:

http://support.microsoft.com/kb/255690