PS: It looks like Tivo has their Home Media Option where you can use a bedroom Tivo to play shows from a local or remote machine. It's new, bleeding-edge but this exactly solves your problem. This link Tivo Home Media Option might shed some light.
Here is problem you need to check: If you go with a modulator and want to combine the signal in with an ordinary CATV feed, you need to pick a channel that is not used by your CATV service. Otherwise you will have 2 full-strength signals on the same channel and the results wont be pretty...