You need to log into your router configuration panel and allow for uPnP configuration. Or forward port 15000 so that it points to your computer's IP and port 15000. You can find instructions for each router here
http://portforward.com/I was just writing a blog post the other day about how this issue is the major roadblock against pulpTunes adoption, and how I'll be addressing this in the next version, check it out:
http://www.pulptunes.com/?p=140