Hi
Im not sure the 450wi is the right solution for your application, but probably the cheapest. The projector is ultra short throw and designed to be mounted on the wall so not sure how you intend fitting it, perhaps on a mobile unit such as loxit, but again not sure that would work. Also a drop down electric screen just wouldnt be sturdy enough and would mive when you use the pen ! You can buy a Promethean (and smart) mobile system that can be moved around easily and has a built on short throw projector that would not require any adjustment when you use it. Or like others say you could go for an interactive plasma, but pricey for a decent size.