function toggleLayer(whichLayer)
{
  if (document.getElementById)
  {
    // this is the way the standards work
    var style2 = document.getElementById(whichLayer).style;
    style2.display = (style2.display=="block")?"none":"block";
  }
  else if (document.all) 
  {
    // this is the way old msie versions work
    var style2 = document.all[whichLayer].style;
    style2.display = (style2.display=="block")? "none":"block";
  }
  else if (document.layers)
  {
    // this is the way nn4 works
    var style2 = document.layers[whichLayer].style;
    style2.display = (style2.display=="block")? "none":"block";
  }
}