You would need an input card to get the TV signal from coax cable into the computer and then there are many programs that work like a DVR. These guys have many devices that would work depending on the quality and features that you want: http://www.hauppauge.com/
not super easy to do. i have included a link for some more info.
You will need to get a tv tuner card in your PC. this will have a slot for a cable card and coax.