I used to be on the exact same set up as you with BigPond....
With your Port Forwarding it's not set up correctly...
You only need one TCP and one for UDP setting and the numbers have to be exactly the same...
ie. TCP incomming 50157 to 50157
....UDP outgoing 50157 to 50157
Your set up within limewire is fine...
Here are the detailed instructions for your modem/router...Also make sure you set up the static IP...If you have already set up one for your computer you wont have to do it again...
Port Forwarding for the Thomson/Alcatel SpeedTouch 530