1. Purchase a TV tuner card. (try Newegg.com)
2. install the card into a free PCI slot. This is the long, white, plastic socket situated towards the back of your computer.
3. Remove the expansion slot cover (metal plate) above the PCI slot you plan to use.
Insert the tuner card into this slot (DO NOT FORCE IT IN. EVERYTHING SHOULD FIT SMOOTHLY).
4. Hook up your television coaxial cable to the correct connection input port on the back of your newly installed tuner card (do not use the connection marked "FM").
5. Plug in the computer. Make sure all cables you disconnected earlier are reconnected.
6. Install your tuner card drivers (usually with the CD provided when you ordered the tuner)
7.Then get Windows Media Center if you can get you hands on it (included in Vista Home Premium and Ultimate). Otherwise use the software provided on the driver disc or buy something else
follow the instructions specific to your tuner card if it differs from the steps above.