Actiontecs are often better off port forwarded. However they do have UPnP options. Try this first. Click the Advanced Setup link near the left side of the page & you will see UPnP option. Port Forwarding for the Actiontec GT701-WG

If you go here PortForward.com - Free Help Setting up Your Router or Firewall you will find it listed at far left column. The instructions are for windows, I hope that is still applicable or similar. The first thing you must do BEFORE port forwarding is set up a Static ip. Without a static ip or if it is done after the PF rules are set, the process won't work.

What is your OS Firewall? Try to make LimeWire/Gnutella an exception for it and perhaps its default port of 6346