Sully you need to go to
http://192.168.1.254 and enter your username and password. i think this is given to you when you recieve the broadband first.
if you dont have it ring eircom and tell them you want it.
the once your in the click on 'Expert Mode' i think its called.
In there somewhere is an option called 'Pinholes'.
You need to add a UDP port and a TCP/IP port to that. Make sure its the same port as you setup your server with. Try 24000.
All this info above is just from memory, i will give you exact details when i get home again and i can look at my Eircom setup.
Let me know how you get on