Have you forwarded that ip addy in your firewall / router?

I have an even simpler version that works on an windows version and allows anyone in your home or work lan to connect to your machine to upload and download files.
http://www.atopo.net/tool_miniserver.php
install this and drag the files you want to share over the network. point your browser to the correct IP address it shows and download away.
As said above youll need to forward the FTP port from your router so the outside world can get in. Dont worry about any further IP binding as your WAN IP doesnt exist as far as the FTP server is concerned. As long as you have the port forwarded in your router the router will pass all the requests to the FTP server, and then the FTP server back to the router and the router back to whatever IP requested the data in the first place.
