This method is good when you just want an extra place to watch your current TV service on your PC. If you are totally satisfied with the TV cable service that you currently have, this may be an option for you. A good tv tuner software will run anywhere from $50-$100, and will include all of the software that you need to get going.
The second method, which is what I use, is to join a service that will let you watch thousands of TV stations online. The only thing that you have to do is join the service, and have an Internet connection. That is all you need.