How to Access Internal Server from outside the Intranet?

Please enable the Port Mapping function and configure as below (suppose the server IP is 192.168.0.66, port is 99):
Dest Host: 192.168.0.66
Dest Port: 99
Port Type: TCP or UDP
Local Port: 99

You can also get a guide with pictures from here:
http://www.youngzsoft.net/ccproxy/faq_6.htm.