Hi Nancy:

To allow syncing to work on, say, port 3169 you would need to enable port mapping on your Airport. For example:
[attachment=0]<!-- ia0 -->Airport-Port-Mapping.png<!-- ia0 -->[/attachment]
In that example, the port at 3169 on your Airport is mapped to port 3169 on the computer at on your local network. That way any communication with your static IP address at port 3169 is automatically routed to your computer rather than being blocked/dropped by your Airport.

John Wallace
Now X Tech Lead
President, Now Software, Inc.