Either your firewalls & or ANd your modem routers NAT which is similar to a firewall. For fireall configuration to allow LW access see here: http://www.limewire.com/english/content/firewalls.shtml

Can you tell us your modem & router brand & model number so we can check to make sure there's no nat devide here. If there is, then we'll need to forward a port (give LW access) for it.