Drywall screw will hold quite will in plaster wall on wood lath. The lath are 1.5" wide and spaced about .375" apart. A sharp pointed drywall screw will usually go right through the plaster and hold in the lath. Of course if you happen to get the place between the lath (the key) the screw will just go right through and not hold. This is usually not a problem. Simply move the screw up or down about an inch and try again for the meat of the lath. This is better than driving nails, because unless you are on or very near a stud the lath will spring, possibly crack, and break the key in that area.