I have a ReplayTV unit, and you have to subscribe to their service to get the channel listings and such. You can pay a one time fee or a monthly fee. I don't know of anyother way around, but then I never looked.
It requires an internet connection of some sort, because it needs to download the tv listings and updates for the machine. I just plugged it into my wireless router with an ethernet [Cat5] cable and away it went.
I really like the ReplayTV, compared to my cable providers DVR unit, as it has commercial skipping and repeat recording. It's easier to search and just more intuitive in its interface.
Hope I've helped!