I just got Limewire to upload past my Linksys router! Here's a solution that worked for me:

Go into your browser, go to 192.168.1.1 and click on the Advanced tab--this logs you into your Linksys router. Then click on the Fowarding tab, forward ports 6346~6347 to your IP address. (i.e. 192.168.1.101) If you're on a Mac this would be the same IP address set in your TCP/IP control panel.

Go into Limewire's Tools>Options>Advanced> firewall and check the Force IP button and then enter your ip address: 192.168.1.101 and port 6346.

Hope this helps! Good luck!