I have a Dish DVR and I would love to do that, but I have read the forums and it is really hard to find anything on it. Forget about Mac compatible.
So I just hooked up my camcorder to the tv, and via firewire to the computer, and put the camcorder in dv bridge mode, played the show off my dvr into the computer via camcorder, you can watch it right in iMovie and record. I recorded the show, fast forward the commercials like I would watching it live, and then after the recording, edited out the fast forwarding of the commercials and saved the movie project. Then just used Toast to burn it to a DVD.