function doInvertSelection( frm, nam ){
  for (var i = 0; i < frm.elements.length; i++) {
    if (frm.elements[i].type == "checkbox") {
      if (frm.elements[i].name == nam) {
		frm.elements[i].checked = (frm.elements[i].checked) ? false:true;
      }
    }
  }
  return false;
}