nortons fine - 
 
Open the following ports to enable Symantec AntiVirus Corporate Edition and LiveUpdate to work correctly:
- UDP port 38293 -- Intel PDS listening for ping packets
- UDP port 2967 -- RTVScan request to Winsock
- TCP ports -- 80, 21, 443 - LiveUpdate
- personally i wouldnt open 80 21 or 443 seems a bit starnge it needs web server ftp and https ..
 
my NAV works fine though a router - im using 2003 but i imagine the live update software/engine is the same
 
2 things you can try.
 
Add your computers IP to the DMZ so basically the router dosnt do any firewall/port fowarding .
 
Remove router plug Modem to NIC of your pc. 
 
in both cases see if Live update works .