on 16-07-2013 12:08 AM
Your router lists all of the devices connecting through it.
Connect your PC to the router then open a browser window and type in the address bar 192.168.0.1. You will be prompted for a user name which is 'admin', and a password which is 'sky' (if you're on sky and haven't changed it). I don't have Sky internet, so I don't know the interface, but in there somewhere it will give you a list of connected devices, with their MAC and I.P. addresses.
If you make sure that your Sky box is the only thing connected directly (with an ethernet cable), and do the above wirelessly, you can instantly see which MAC address corresponds to the Sky Box