In my experience, Limewire only uses 6348 if another p2p software already uses 6346. Are you running other p2p software concurrently with limewire?

If I remember my time using norton fw i had to allow the program to access the internet, not just open the port. When I ran limewire the first time, norton asked whether i wanted to allow 'sun microsystems java something' to access the internet. Norton doesn't recognize lw as limewire.

hope that helps, good luck!