Shoot, Julie...I'd have to open my PE up at my computer at home, so I couldn't even give you an immediate answer
However, a quick thought that does come to mind is to use the "Layer" function..the first photo is the main "layer", but you can add to that by putting other things (photos, text, drawings, etc.) on the different layers..kinda like Illustrator does it.
Hope that's a start at least!