I can show video in picture-in-picture mode on the HP LP2475w monitors I have. Vide inputs are composite, S-Video and component video. So if the second computer is able to produce component video, then I can either have a small PiP window (maybe up to 1/9 of monitor) or split the monitor horisontally in two. The PiP window is good enough that it can be used to keep track of a running program and see if it has stalled and needs input, but it's too small for it to be comfortable to read the text.