Try reconfiguring the Norton firewall - remove the current LW rules & then add new ones. A couple of links here which might help...
http://www.gnutellaforums.com/226610-post6.html
PortForward.com - Free Help Setting up Your Router or Firewall

There are lots of connection fixes to try in this thread: If LW Will Not Connect
Start off by deleting LW's preferences folder (that thread has a link with info for Vista users). If that doesn't fix things, the next thing to do is replace your gnutella.net file

If none of the fixes in that thread work, look at port forwarding for your router. The instructions are here: Port Forwarding for the Linksys WRT54G
First of all, you'll need to set up a static IP address: PortForward.com - Free Help Setting up Your Router or Firewall
LW's listening port, port in the 'manual port forward' box & port forwarded within router setup all have to be the same number
When LW was connecting ok, did you still see the firewall icon?