There are different ways to get TV to your computer. One way is a USB-thingie which recives only digital signals usually, while there are cards can recive analog signals (I got one). The cards need to be fitted in the computer, it's not hard and mpst people can do it themselves. You also need a software. For the card version you also need a antenna, while the usb digital recivers usually don't need one.
EDIT: groessl35, I think those only capture signals from a TV, not display TV on the computer itself.
EDIT2: I use a
Hauppauge PCI card.
/ 
