Sounds if you're triing to let you'll friends play over a dial-up line (maybe cable modem as well). they could use
http://www.dyndns.org/ along with a VPN client and you could set up VPN server on firewall or machine with Minilogin. To be honest, I haven't done this yet myself, but am planning to once I get a somewhat stable server up and running.
P.S. Dial up sUx0rz - get disconnected most every time you zone..