1. What brand & model number of devices are you using?
2. Did you enable UPnP on your Airport? (it's actually a little different to UPnP.)
3. Which operating system are you using? I'm guessing you're using mac OSX right? Which version?
4. Do this simple test for us. Using your browser go here:
http://www3.limewire.com:6346/ The page should say 'Your test worked!'. What happens when you go there?