One useful definition for what is portable is the size of an airline carry on bag:
Cabin baggage should have maximum length of 22 in (56 cm), width of 18 in (45 cm) and depth of 10 in (25 cm). The sum of these three dimensions should not exceed the 45 in (115 cm). These dimensions include wheels, handles, side pockets, etc.A typical Carry On Watertight Hard Case is the Pelican 1510, which is
From: Luggage, Wikipedia, 22:05, 26 July 2007.
19.75" x 11.00" x 7.60" (50.1 x 27.9 x 19.3 cm) inside.
A flat panel screen such as an LCD or plasma display will not fit in a travel case. Also the large plastic or glass surface of the screen is subject to damage in transit. An alternative is a projector, DLP Projectors currently offering good brightness at a reasonable price.
Laptop computers are more easily packed than LCD screens. In this case high power computers are not required. An alternative is the ASUS Eee PC which has no hard disk and a 7" or 10" screen.