Battle.net server

[linux]

I was wondering if someone could shed a little light on a matter of 
DHCP routing for me. I'lkl try to be as coherent as possible, but I'm 
warning you I'm very new at this.

I have successfully set up a Battle.net server and everything is 
working great, but...

Can someone tell me IF I WANTED TO, how would I access the server from 
an outside computer? For instance:

My server is behind a router. So what I want to have happen is for 
someone on the internet to access my server(a friend of mine at his 
house). The router is broadcasting XXX.XXX.XXX.XXX as the ip address 
but my server is locally YYY.YYY.YYY.YYY. What would the address be if 
I wanted to give it to someone to play a game?

OR

Do I have to be outside the router to do this?

Christopher