The whole point of the way mythtv is designed is basically:
1. Get a hulking great server PC with capture cards and noisy disks.
2. Install and configure Mythtv backend on server.
3. Hide said hulking great server PC in basement/cupboard/garage out of sight.
4. Procure small, quiet, lowpower, thinclient PCs and place in proximity of viewing device.
5. Install and configure mythtv front end on said small pc.
6. Repeat steps 4,5 for as many veiwing locations as required.
7. Relax and enjoy centralised media storage and configuration with the ease of expandibilty a server/client setup provides.
But there are other ways as mentioned above. One way which has worked nicely for me, although I don't do it currently, is to get a TV out card on the mythbox. Feed this into a modulator box (~£20) and pipe this into your coax aerial feed that goes to each room. Just tune each TV into whatever channel you set on the modulator. But this won't work so well for HDTV.