What I don't have a clue about is have the 'main' load the background image (1024x768) and have the unique instances use viewports 'onto' that image.
Does this mean you want each blitz "process" to be able to draw on parts of the main image (on the "main" or "server" process), or you want parts of the image to be copied, becoming the main canvas on each "sub" process?
Would this be a full-screen application?
One of the things that comes to mind is why you must have each subprocess draw -- why can't you send a message to the main process and have it draw on its own canvas.