My Ninjam server works only locally

[jooowy]

Hi everybody
I've been trying to setup a ninjam server on my computer and everything looks fine except that when I want to connect with the ninjam client, I can connect only with my local IP address (192.xxx.xxx.xx) followed by :2049. It won't work if I do the same with my computer's network IP (89.xxx.xxx.xx). Other people can't connect either. It might be related to firewall or any port opening problem in the modem but I know nothing to that and so far I wasn't successful when working with that.
Any help?
My internet connection is through a modem / router where I can setup firewall preference, nat and dmz rules. I am running OSX 10.3.9.

[DaMNeD]

Set up your nat/modem/firewall config and forward tcp/2049 port external interface to the ip address of your mac locally.
And if you're using mac firewall, authorize port 2049/tcp outbound connections