Thanks for the added advice and thoughts. The Sky Decoder is a silver box with SCART ports on the back of it so it isn't HDMI compatible. If I go back to SkyTV will they have a lead to supply me with or is best to go and buy something?
It sounds like the Pace box I used to have. In which case it will do component video, and you just need a SCART to component cable. Try Sky first, and they may just send you one - mutter about cancelling if they don't, they will want to keep a paying subscriber.
Otherwise, online or a good electronics shop like Jaycar should be able to sell you one for a few tens of dollars. I can't remember whether there is also a setting on the box to make it output video as component, but Sky should be able to walk you through that over the phone.