I've seen such devices, they had one at a conference I was at once, where you had 2 laptops plugged into a projector via normal monitor ports, and just turned the switch to change which laptop was displaying on the projector. No idea what the thing is called Try looking in computer magazines on the ad pages, they tend to have more exotic equipment there.

Or get a 22" monitor from Mitsubishi that has two inputs, and use the OSD on the monitor itself to switch between inputs


Also, I don't see why a machine should hang if you unplug the monitor cable, the video card must be pretty ancient or something if it does that