first thing you said you wanted is a motor. do you have that picked out yet? however you plan on doing the actual moving is a good place to start. once you have that you can check out www.sdp-si.com for small nylon gears, worms, and racks you're likely to need.
Also, check out http://www.firgelli.com/products.php for linear actuators in case you have trouble putting gears together.
Once you've got that much, you can start figuring out how that motion (linear or rotary) translates into moving your screen the way you want to.
Hope that helps get you going.