In LW, go Tools > Options > Advanced > Listening port & make sure that LW's Gnutella port & port in the 'manual port forward' box are the same number. If they're not, change both ports to the port number that you forwarded within your router & then click 'ok' at the bottom of the page.

And as LOTR said, you'd need to first have a static IP set up for your computer in order for port forwarding to work. In case you missed this step, the instructions are here: Setting a Static IP Address in Windows XP - PortForward.com

If neither of those suggestions help then maybe we need your system details in order to have a better look: System details - help us to help you -> Provide these details when you post!!!

Check underneath your router & see if there's a model number listed, apart from the one that you posted earlier.