Yes you have to set up port forwarding in your router.
. First you have to set up your computer that serves files to have a static IP by using the "Add DHCP Reservation" form here http://support.dlink.com/Emulators/dir655/132NA/Basic_Network.html
. Then you can use this guide to set up port forward http://portforward.com/english/routers/port_forwarding/Dlink/DIR-655/HTTP.htm
with "IP Address" as the IP that you reserved in previous step. You should be able to access your server then from outside.
. (Optional) In case your ISP assign you dynamic IP, you should use a service like DynDNS to setup a hostname so ppl can get to your server using the hostname. It's more convenient like that. Relevant links: http://www.dyndns.com/
and setup in your router http://support.dlink.com/Emulators/dir655/132NA/Dynamic_DNS.html
Anyway, my set up is like this and hfs works fine here.