Best solution in this scenario is to install DC from media, a new feature introduced with windows 2003 server. You have to take the system state backup of current Global Catalog server, burn it on the CD/DVD and send it to the destination (remote location). On the remote server which needs to be promoted to be DC restore files to Alternate Location and Run, type dcpromo /adv.
For more information please read: http://www.petri.co.il/install_dc_from_media_in_windows_server_2003.htm
