Two computers using the same port? My immediate thought is 2 suggestions. Go to LW's menu Tools>Options>Advanced>Firewall & set it to UPnP. If that doesn't work then try setting a different port for LW to listen to; eg: Port 6342 (sample image here though this is for force ip so just set that to UPnP for now:
http://www.gnutellaforums.com/showth...010#post120010 )