Thanks for your post.
The feature you are looking for is called port forwarding. It basically rerouts a request by the web connection to your router to the correct internal IP address it assigns to your computer on the port set up in the forwarding. This keeps the remaining ports closed on both the router and the system, and adding passwords to the database increases the security to that file as well.
Apple can provide directions on how to set up the port forwarding for your router. The port to forward to on the internal IP for your system is port 80 (or 591, as determined by the setup in FM Pro).
Please keep me posted with any further questions on this issue.