What i did when i was running just 2 instances is go into your video options and rotate your display 45 degrees, then your monitor is meant to be unscrewed from the stand, spun around and rescrewed so its up and down rather than side to side. then on the maximizer just divide your current resolution in half and put both instances at the same resolution but one on the top half the screen and one on the bottom half

i did this with my 19" but instead of it being 1440X 900 it was 900 x 1440 both wow clients were at 450x720(in keyclones maximizer) the ingame resolution was still 800x600 hope this helps