windows service advertising protocol problem

I have placed a Windows 2003 server, running SQL Server 2000 on a DMZ that is
on my internal network. I understand that as a Windows system starts, it
advertises its services through Service Advertising Protocol, which allows
client computers to browse and select servers of a particular type (in my
case SQL Servers). Is this just a broadcast, or is it registering with
active directory? What firewall rule needs to exist (what port or ports do I
need to allow) to enable that server to advertise that it has SQL Server to
clients on another network connected to the firewall?

Thanks,

J