To use your old sky box - you need a cable up the the dish from it - and a dual LNB (that's the bit on the end of the dish.) - which has connections for two cables.
Then it acts just like you've got two independant dishes, and you'll get all the "free" programs from your old sky box - there's lots of them!
Or - you can change the cables about so that your terrestrial aerial cable goes directly to the second TV, then you'll get all the normal terrestrial channels on it.
The one thing your sky box cannot do is give you terrestrial channels.