Look on your SpeedTouch & see whether there's another number showing (something like 510, 530, 536 etc), have a look underneath too.

If you can find your router model in the list here, then choose LimeWire from the list of programs ...
PortForward.com - Free Help Setting up Your Router or Firewall
... you'll find step-by-step instructions for port forwarding
Don't forget to set up a static IP address if that's part of the instructions. LW's listening port, port in the 'manual port forward' box & port forwarded within the router setup should all be the same number.

Go back to the gnutella.net file that you replaced, hover your mouse over it...what size is that file?

You could also try changing ports. In LW tools > options > advanced > firewall config. Change LW's listening port to 65000 (or any port in the range of 49152 - 65535) > apply > ok.
If you change ports within LW, you'll also have to change the port number forwarded within your router.