You can do this using a couple of different methods but in the end, you are going to run a high resolution signal across coax which will result in sub-standard (standard being S-Video or better) video and audio. Though I understand why you'd like to do it, I'd stick with a DTV tuner in each location but if you must;
1.) Use a modulator to "modulate" the output from one (or all) DTV tuners throught the coax to the TV's. Modulators allow you to input a signal across coax and select a channel to view at the other end it using the TV's onboard tuner (similar to a VCR using channel 3 on the TV to view).
2.) Use an infrared "injector" to pass IR signals down the coax to the centrally-located DTV tuner to "change the channel" or other DTV menu options. This requires an infrared seperator and emitters on the back end to "repeat" the remote signals passed through the coax to the DTV tuner.
3.) Alternate to #2 - Run 4-strand wire to each room and put an infrared receiver in the ceiling of each room to pass the IR signals back to the DTV tuner (also requires infrared emitters at tuner-end).
4.) Alternate to #2 and #3 - Buy a remote capable of sending radio rather than IR signals and simply use emitters on the DTV tuner to convert the radio signal into IR.
The bottom line is you'll spend money and end up with issues like all tuners changing the channel when one button is pushed in one room. DTV tuners turning on or off when someone else decides to turn theirs on (or off). Also, the biggest drawback (IMO) is the lack of decent audio and video since your modulating the dignal across coax, this is not that great (I speak from experience as this is the way I set up my first multi-room system in 1998). The picture was more than fine to watch but crap when compared to 1080i output from a progressive scan DVD player across HDMI cables...
I hope this helped a little but the others are right in that you should probably consult a profesional if you want performance over price. If you want price over perofmrnace, this can be achieved (with a steep learning curve)...
