I find these rules allow Gtk-Gnutella to connect and work fine
Code:
iptables -A INPUT -p tcp --dport 6346 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 6346 -j ACCEPT
6346 is the default port for the gnutella network but you can choose a different port, just make sure you select the right port on the network tab in Gtk-Gnutella