For more information about these projectors, google for "pico projector" (units
little larger than a big cell phone) or "pocket projector" (units about 5 inches square).
Some have built-in battery that runs the machine for a couple of hours, others run
off AC through a power brick that converts to DC. The projectors connect to a computer
or media player using a VGA port. Some have USB ports for connecting cameras or
flash drives.
Here's a web page that describes several pico projectors seen at CES in January.
http://www.fastcompany.com/blog/noa.../10-tiny-mighty-pico-projectors-photo-gallery
John is right, the projector is much lighter, smaller and less vulnerable to damage
than a standard LCD screen. Drawbacks include image is not as bright or as detailed
as an LCD, and for these reasons the projector is not a good alternative for computer use.