On the PC on which your are running the EQ client, you probably need to edit your hosts file:
C:\windows\system32\drivers\etc\hosts on xp
and add an entry:
192.168.x.x (or whatever your LOCAL IP is) <your server's DNS name>
I am assuming your are using your server's DNS name rather than an IP address in your server INI and BAT files.
E.g., my server DNS name is rama.demon.co.uk and my server's INTERNAL IP is 192.168.1.100, so I added this to the C:\windows\system32\drivers\etc\hosts
file on the PC on which I run the EQ client
Code:
192.168.1.100 rama.demon.co.uk
Without this I will get the symptoms you describe, i.e. people outside my network can logon but I can't.