I worked up a rough prototype of a 19" system, but decided it was too small. I'm waiting for a good deal on a 32" LCD before I do it.
I used an extremely lower power motherboard. I think it was an EPIA mini-itx board running at 500mhz.
I used a laptop drive, but I think when I build it again, I'll use a CF card as a boot drive instead. I'll build the machine with a hard drive, whittle it down to the bare minimum needed to run, and then ghost it over to the CF card.
With an extremely low power motherboard/cpu and no hard drive, power consumption should be below 20 watts, not including the display.
For the display, I plan on stripping off the plastic shell and building it into a matted frame. Of course, even with a very lower power PC and an LCD monitor, you still need to get the heat out of frame. I'm debating several options.
Option number one is to just use some small fans and vent the top of the frame backwards into the wall. I've got to cut into the wall to run the cables anyway.
Option number two is to build a large heatsink into the frame or even make the entire frame from metal and just dump heat into it. This sounds like the best solution, but I don't have the skills to implement it.
Option number three is to just go traditional and have some slots for air intake at the bottom of the frame and a few small fans and slots at the top of the frame for expelling warm air.
The final option is sort of a copout. I'm thinking about just mounting the 32" TV with a traditional mount and feeding photos and video to it from a nearby dedicated computer running the cables through the wall. It's the simplest and most practical solution, but the least cool.