I have been doing this for a year I have been using my Xbox 360 as an extender with my home theater PC running Windows Media Center. I have been using a quad tuner Centon card that uses a CableCard. Using the Xbox as an extender allows me to watch any recorded show and live tv across the network. Even HD channels.
Plus having my own equipment (CableCard device) I get a credit of $5 each month from Comcast and the CableCard is free.