var current_layer;
current_layer=null;

function showHideObject(t) {
  if(document.getElementById) {
    layer_object = document.getElementById(t).style;
  } else {
    if(document.all) {
      layer_object = eval('document.all.'+t+'.style');
    }
  }
  layer_object.visibility = "visible";
  if(current_layer && (current_layer !== layer_object)) {
    current_layer.visibility = "hidden";
  }
  current_layer = layer_object;
}