I have the same setup (IP Camera) and it works wonderfully and I can access it externally. I am using SME server 6.01.
This is how I did mine.
IP cam address is 192.168.2.2, and I am using port 81 to access it internally and externally.
Port Forwarding menu
TCP, port 81, 192.168.2.2, 81
Next, make sure your camera is also set to be browsed at port 81.
You're done. I hope this helps ya.
Archangel