For a start Java 1.3 is way out of date & I suspect the other version you have will be 1.4.2 or 1.5 To find out go to LW's menu Help>About LW & this will tell you the version of Java as well as the version of LW.

Perhaps your modem-router does not understand UPnP. So let's do this manually. Go here: http://www.portforward.com/routers.htm & choose your model which will be on the far right half-way down page. Click on your model (there's 4 models with similar no. eg: USR8000A.) Now on that following page click on Port Forwarding. Then click on the Static IP link. You must set up a static ip before you forward a port (open a port.)

Steps:
1. Set up a Static IP (direct link to instructions for setting up static ip)
2. Forward Port 6346 as described at portforward.com
3. Force IP within LW: Force IP instructions & sample image & 2 posts after that.

After this you should be able to access port 6346 which is what LW uses. LW should now work.

Make sure you configured Norton correctly; see: Configuring Norton Internet Security & even though your XP firewall is disabled, configure it for LW anyway: http://www.limewire.com/english/content/firewalls.shtml

After this give LW some time to try to connect. Perhaps even manual connect might be wise. Make sure your Java is up to date if it's not.

If you can't connect after this then I'd wonder about your ISP. Who is your ISP by the way?