If it's not listed then yes, you add Gnutella/Limewire. It does sound as though Tiger has new firewall settings. I'd suggest port 6346 for both UDP & TCP in the same way you'd do it if you needed to forward a port on a router. Advanced Tiger firewall instructions:
http://www.macdevcenter.com/pub/a/ma.../firewall.html
The only references I can find are for Panther & earlier's firewall.
http://www.gnutellaforums.com/showth...422#post174422
& the one below which is only partially helpful.