^ You need to port forward, currently your on your localhost.
For guides on portforwarding check out portforward.com or if I'm on msn then you can pm me and I'll help you out.
It's pretty simple though... basically, go into your routers page - find applications/gaming (Different on some routers) ... It should look like
Incoming port - Outgoing Port - Protocol - IP - Enable
^ Or something similar to that..
For your incoming and outgoing port type in the same four digit number. This is the port they would enter when entering your server.
For your IP... it should be similar to your routers IP.. Type in the three digit (sometimes less) number that your computer is using on the networked server. i.e. I use 192.168.1.101, while my brother might use 192.168.1.102...
Then change the protocol thingy to either "both" or if you do not have a both option you would have to make two of these, enabling them both.
Then enable em, and click save settings... That should do it.