Toggle bolts. Should require a half inch hole drilled through the drywall into the stud. Insert the toggle, get it snug, snap off the excess (the ones I use are plastic with a metal end where the screw goes). Test the toggles by taking one of the screws and make sure it screws in to each toggle. Sometimes you'll get a bad one or it'll be slightly crooked and won't screw in. You don't want to get 3 bolts in then find out the last one is no good and you gotta redo everything. Hold up the mount, put in each bolt, then screw them tight.
Gotta be some sort of professional LCD screens meant for combining like that. Using any regular TV would cause bigger lines in between them because TVs have bezzles at least on the bottom, sometimes all the way around.
