Did you go to the LW test page?
http://www3.limewire.com:6346
What did the test say?

I can't find any info to tell me whether your modem uses UPnP. If it does, you'll have to enable it within your modem as well as within LW.

If there's no UPnP, you might have to forward a port through your modem.

Try & find out about the UPnP first though