What kind of hardware are you planning on using? Are you going for a small compact form-factor pc?
To my understanding, centos 5 is very similar to red hat, is that why you chose this particular distro? I have been very excited for the hardy heron release - everything is becoming more easily compatible and they cleaned it up a little. I have been brainstorming ideas very similar to yours, concerning functionality towards Car Computing. using a panel to switch desktops for different operations. I always thought of the idea of a "Live" desktop. Using desklets to monitor speed, gps directions, and music information, while layering the background as an app - like ig
I think myth would be perfect, especially for as much video you have. seems very touch screen friendly.
your monitor situation seems a little complex in my opinion, though well thought out. i have never tried rotating a cube with multiple monitors. I am curious to what video card you are considering.
this seems like a good project, i would like to see what progress you make with it.