The way I do it is via the network and my TiVos, so this may not work for you. The TiVo in my main room is hooked up to my cable (well, FiOS), and does all the recording. It is connected to the network wirelessly. The TiVo in the other room is hooked up to the network via ethernet, but that's just because it's in the same room as the router. It could be wireless, too. From the second TiVo, I can copy over shows from the primary and watch them that way.
However, that doesn't give you real-time TV watching. I think if you had a second cable box in your main room and a SlingBox hooked up to it, you could then send the signal from that to a SlingBox hooked up to the dinette. The downside with this is that you will need to rig up something crazy (I think) in order to actually do the tuning from the dining room.
That's really the main problem here. There are many ways to get a video signal to the TV, it's just being able to adjust what you're watching.
