I have plaster myself. There are studs behind the plaster walls just like drywall. In addition to that though there are generally wood lathes that the plaster adheres to. These are hung in a horizontal fashion. To hang heavy things i use toggle bolts. It is bascially a bolt with a spring nut on it. You drill a hole, compress the srping nut, shove it throught the hole and the nut springs open. This is a one shot deal. After it springs open there is no way to get it without damaging the wall. I have used these for many things and had never had one fail. They can be purchased at any hardware store such as lowes or the home depot.