LW's firewall setting for a UPnP capable nat router should be set to UPnP for ease (so you don't need to manually forward a port on your modem/router.) Otherwise yes you can manually configure your devices to allow port 6346.

I do believe there is a bug in LW 4.6 with UPnP (see: http://www.gnutellaforums.com/showth...threadid=34327 but don't know if that applies to you.) LW 4.8 has been released but don't know if it's solved the problem yet due to the history page not being updated yet.