Can someone guide me on how to connect DirecTV to my desktop computer so that I can watch from my computer and also use it as a DVR?

I currently have four lines from coming from the dish, 1 is connected to an HD DVR receiver, 2 is connected to a normal receiver, and the 4th is not connected to any receiver. The 4th line is the line I would like to use for this purpose.

Thanks in advance!