Firstly you need to set up the port forwarding. See Port Forwarding on HH2 for instructions. Make a note of the IP address for the slingbox.
Then you need to go to Set up Slingbox , create a slingbox account if you haven't already done so, and follow the instructions. If you have any problems with the software connecting to your home hub, try the "skip this step" route and enter the details yourself. I had this problem and the issue was the slingbox software assuming an IP address which was not correct, so I changed it to the one noted above. I'm now able to view over the internet (and on my mobile phone too, which is great!).