Try PortForward.com for some help. Direct links are below:
http://portforward.com/english/routers/port_forwarding/Apple/AirPortExtreme/HTTPS.htm
http://portforward.com/english/routers/port_forwarding/Apple/AirPortExtreme/HTTP.htm
and you can open 4125 as well (the others above are 80 and 443)
Keep in mind your ISP could block ports, or you could have another router in the "chain" causing issues. For detailed walkthroughs on your MediaSmart, you can review some of our tutorials on the HP MediaSmart server at
http://www.MyHomeServer.com