Depending on how large you really need the image to be, you could buy a couple of cars for what you'd spend on the projector.
You might call a local staging company to discuss your needs and rent/set up a projector, screen, and dress kit.
As a side note, we run all our presentations on two computers, a main and a backup (with a high-res switcher), to protect against the possibility of a computer crash.
Walter Soyka, Principal
Keen Live, Inc.
Presentation, Motion Graphics & Widescreen Design
RenderBreak: A Blog on Innovation in Production
