there are probably several people online when you are posting, but most choose to use an "invisible" option so that they can't be seen at the time and can reply to messages at their convenience...most everyone will tell you your best bet is to get ICQ and form a list of civ players...i have done this with the MP list on this site and already have enough players listed to usually be able to start a game whenever i want with at least SOMEBODY...
per the IP address issue, it seems your real question was how does the host find out his IP address to give the players: when a host starts a game, the GAME ITSELF tells the host his IP in case he doesnt already know, and then the host uses ICQ to message that address to the other players, yet another reason to get ICQ...of course you could do all these things with email, which would needless to say take a very long time, or you could use any other message system like aolmessenger or yahoomessenger, but ICQ is still the best because its the most widely used among civ players.
you really should get ICQ, and then add me, pigpen: #171312317...i'm ready for a game right now =)