Managed to get SKY OD via laptop to work. I had to change the IP address manually on sky box to one that was different from my laptop.
So if anyone who wishes to set up OD using this technique. It works using a desktop PC also, so here is the procedure below. Instructions below are used with windows 7.
1.Connect Sky HD Box to Laptop via Ethernet cable
2.In windows 7, Go to Control Panel> Network and Sharing Center>Change Adaptor Settings.
3.Highlight WiFi and LAN connections and right mouse click and select "Bridge Connection"
4.Go into Sky HD box "Settings" menu and go to "manual IP config" and change IP address
5.On Demand should now work.