Oh dear its very simple and their are instructions on
http://btybb.custhelp.com which is BT's help site. Search for port forwarding home hub. It has been updated to accommodate the latest version.
You mention being able to administer the router from the internet, the remote administration turns off after 15 minutes so that if somebody in experienced turns it on it does not get left open and subsequently hacked. BT have also configured it to give out a random password each time but it can be changed.