I'd like to combine the signal from my Dish Network DVR that goes out via coax on Channel 3 to one TV and 73 to the others. I'd like to have a single cable in my house that carries those two signals plus the signal from my CM 4228. I have an LG HDTV that has an ATSC tuner, but the LCD upstairs only has NTSC and will need a digital converter box, I'll also need one to power the HD signal to my LCD projector in the basement.

Maybe these images will explain it better. Is this possible? What sorts of joiners or combiners will I need? Should I just break down and subscribe to the HD service from Dish, and then plug in my antenna to their box to get all the other locals?

Current setup (http://img504.imageshack.us/img504/5189/residentialvideodistrib.png)
http://img504.imageshack.us/img504/5189/residentialvideodistrib.png

Theoretical Setup (http://img219.imageshack.us/img219/5189/residentialvideodistrib.png)
http://img219.imageshack.us/img219/5189/residentialvideodistrib.png
Thanks

It all depends on whether the OTA signal can live on the same coax with the signal from the Dish STB without interference. You could try a regular splitter in reverse to mix the dish coax signal with the OTA signal - try it on the LG TV to see what you get.

Does hooking up a splitter in reverse actually join the signals?

You need to use a pair of diplexers. See: http://www.aeonsat.com/diplexer_guide.php

Does hooking up a splitter in reverse actually join the signals?
Maybe not as well as a diplexer but if there's no overlapping signal on the two coax lines it might work. Most folks have a splitter laying around so it costs you nothing to try it out.