you have to look for a line out on your digital box that looks like an aerial socket and plug a cable from that to the line in socket on the video that also looks like an aerial socket.it should have line in and line out written by each socket.or scart leads which are direct and easier just plug them in. if you dont have a free scart hole on either video or cable then get a double adapter from a electrical shop.
sorry just read the bit about the built in digi box tuner thingy. you should just be able to plug a patch lead between your tv and video. as normal.
good luck.
arry