I'm not sure about limiting the image to certain areas... but to make something look sketchy, go to Effects > Artistic > Pencil sketch and that should work fine.
Or open the image, then open the other one you want. Then copy the second one, and place it into a new layer over the first image. But the second layer was to be set to overlay - or a setting which displays both of the pictures at once.
I'm not sure what you mean - but is this it? When you open an image and its in the box in the top right corner, then open another image and its in a different box in top right corner?
I can't get to that part, I'm not sure what I put into the "Effects" folder. Do I put the whole folder that I downloaded from Flaming Pear, or is there a specific file that I only put in there?