Note: if you have a router you should update to LW 4.4 and up. With UPnP (universal plug and play), LW now does the port forwarding automatically for you when your router supports UPnP. --look into your manual or search google to see if your router is UPnP compliant--.
You have a router that doesn't support UPnP or you want to do port forwarding manually? This site has all of them and explains how to forward a port (In case of gnutella, it is 6346)
http://portforward.com/routers.htm
To get a static address (for stable port forwarding that you won't have to change in your config once in a while):
http://portforward.com/networking/staticip.htm
If your port 6346 is blocked, or you want variety, nothing stops you from using another port: once unfirewalled you will still get the same results as if you forced the port 6346.
If you are using LW, go to options > advanced > firewall (set to port 6346 if not already) and check the option to manually configure the port below the same preference window --select the same port as above, default is 6346--).
If you want to see if you are still firewalled in LW, then go to options > error reports > click on 'see an example':
If the following line says, "Received incoming this session: true", congrats!
You are now fully open to gnutella...
If it says no, something went wrong... Check again all the steps to get unfirewalled to the port 6346.
Bonne chance à tous!
Edit was only to help with a few clarifications.
I didn't change anything, Doc ! Honest !