if (document.images) {
  var imgMin = new Image();
  imgMin.src = "b_minimize.gif";
  var imgMax = new Image();  
  imgMax.src = "b_maximize.gif";
}	
function toggleFilter(img, nr) {
  if (img.alt=="Minimize") {
    img.src=imgMax.src;
    img.alt="Maximize";
  }
  else {
    img.src=imgMin.src;
    img.alt="Minimize";
  }		
  if (document.layers) {
    current = (document.layers[nr].display == 'none') ? 'block' : 'none';
    document.layers[nr].display = current;
  }
  else if (document.all) {
    current = (document.all[nr].style.display == 'none') ? 'block' : 'none';
    document.all[nr].style.display = current;
  }
  else if (document.getElementById) {
    vista = (document.getElementById(nr).style.display == 'none') ? 'block' : 'none';
    document.getElementById(nr).style.display = vista;
  }
}