Best way to get digital tv on my computer?

I've just set up my new Advent T9317 with built in tv tuner. In Media i can get terrestial stations by plugging a portable tv aerial into the aerial input plug-in. In my front room i've got Cable from Telewest. Would i have to run a lead all round the house from the set top box? And then i wouldn't be able to watch a different channel than was on in the front room. My internet connection is via a Webroot external modem plugged into a USB. Whats going to be the easiest and cheapest way to get digital tv and be able to watch a channel independant of my present set top box?