See the info in the User Guide http://www.limewire.com/english/content/userguide.shtml

If the OSX default firewall is on, that can mean extra steps for connections. Check the Preferences->Advanced->Firewall->Force IP to see if that helps. You can also open the OSX Firewall in System Preferences->Sharing->Firewall->New->Gnutella/Limewire (6346)