If I can't find an old console radio pretty soon, I think I'm going to mount my touchscreen on the wall. Here are some things I was considering:
I was considering manufacturing a 'wall box' that would mount to the wall above an existing electrical socket. You can open the wall up and mount a new recessed electrical receptacle (sometimes called a clock outlet) above the existing socket, running the romex off of the existing socket. This is the way some people mount their plasma TVs.
Run the USB/VGA/AV cables through the wall from the location of the screen to where you are keeping the PC (from what I gather, you cannot run electrical cords through walls, hence the clock receptacle). In the room where you keep the PC, you can mount a new USB/VGA/AV receptacle and then just plug it in.
For speakers, I was contemplating mounting them in the corners of the room using speaker brackets and hiding them with those speaker wire corner moldings. Probably hide the woofer somewhere discreet.
Like I said, I haven't decided to mount mine, so that's why I don't have all the details spec'd out, but those were my initial thoughts.