function toggleLayer(whichLayer)
{
  var elem, vis;
  if(document.getElementById) // this is the way the standards work
      elem = document.getElementById(whichLayer);
  else if(document.all) // this is the way old msie versions work
      elem = document.all[whichLayer];
  else if(document.layers) // this is the way nn4 works
      elem = document.layers[whichLayer];
  vis = elem.style;
  // if the style.display value is blank we try to figure it out here
  if(vis.display == '' && elem.offsetWidth != undefined && elem.offsetHeight != undefined)
      vis.display = (elem.offsetWidth != 0 && elem.offsetHeight != 0) ? 'block' : 'none';
      vis.display = (vis.display == '' || vis.display == 'block') ? 'none' : 'block';
}