Problema ADSL para jugar ONLINE a DOOM 3

Tengo instalado ADSL 256/128 de Teléfonica con el router 3com 812. En el juego hay la opción de jugar online pero no soy capaz de ver servidores en la tabla del juego. He mirado por mucho sitios y lo más que he encontrado es esto:

Answer
If you do not see any entries in the server list, do the following:
1) Verify that you are connected to the Internet.
2) Choose Internet for the source in the game.
3) Click Get Refresh List.
4) Ensure that in Multiplayer Option that the Connection is set to your particular connection speed.

If you are still unable to retrieve a list, ensure that you have no firewalls active, and that you have a direct connection to the Internet. This would include disconnecting any routers/hubs or hardware proxies.

Further, due to the variable nature of DSL/Cable connections, it is exceedingly difficult to offer generalized information. In these situations ensure the following:
1) The TCP/IP protocol is only bound to the NIC which the internet connection relies on.
2) The IPX/SPX-compatible, NetBEUI and NetBIOS protocols are not bound to the NIC which the internet connection relies on.
3) In general, we do not advise setting up a Doom 3™ server on a machine that is also either a NAT server (such as Microsoft's Internet Connection Sharing) or set up with ipForwarding for a Local Area Net (LAN) onto the Internet. These machines see clients on your LAN as different addresses from the Internet and thus you cannot authorize these clients.

If you are using a hardware firewall or software such as ZoneAlarm® and you are experiencing problems, make sure your firewall or firewall software is set to allow UDP packets on port 27666 (use port 27650 if you are trying to run a server). Doom 3™ uses this port for connection, message of the day, server browsing, and so forth.

Si alguien me puede explicar que debiera configurar para poder jugar se lo agradeceria. Disculpen mi ignorancia.

Salu2