We did this when we were living in a travel trailer while our house was being built. All you need is a TV source (cable, satellite or antenna) and a TV card (most are PCI and you have to open the computer to put it in- very easy, or some are external and you can plug it into a port on the outside). The TV card will give you an input just like on your TV (coaxial, s-video, composite etc depending on the card) and you just plug in your cablebox or whatever just like you would into your TV. The card will come with software to watch TV on the computer. ATI makes a bunch of cards and you can decide how much to spend- in our case it was as cheap as possible as we knew we wouldn't use it once we were in the house. Worked well for us. We also used the same set-up to convert old VHS videos to digital.