Today, somebody ask me for Win2k3 _msdcs delegate, here is the explain:
These DNS records beginning with an underscore are for servers to locate resources, for example _GC, means Global Catalog and _DC means Domain controller. While these resource records exist in Windows 2000, in Windows Server 2003 these _MSDCS records have been moved to their own zone. The benefit of this new arrangement is that you can control the resource replication. For example, you may want to replicate records to all Domain Controllers in the Forest, or perhaps you want to restrict replication to Domain Controllers in the local domain.
from : http://www.computerperformance.co.uk/w2k3/services/DNS_new_2003.htm