if (document.images) {
  tanja1          = new Image();
  tanja1.src      = "images/tanja1.gif";
  tanja2          = new Image();
  tanja2.src      = "images/tanja2.gif";
  unterricht1     = new Image();
  unterricht1.src = "images/unterricht1.gif";
  unterricht2     = new Image();
  unterricht2.src = "images/unterricht2.gif";
  galerie1        = new Image();
  galerie1.src    = "images/galerie1.gif";
  galerie2        = new Image();
  galerie2.src    = "images/galerie2.gif";
  kontakt1        = new Image();
  kontakt1.src    = "images/kontakt1.gif";
  kontakt2        = new Image();
  kontakt2.src    = "images/kontakt2.gif";
  }
function IOn(imgName) {
  if (document.images) {
    document[imgName].src = eval(imgName+'2.src');
  }
}
function IOff(imgName) {
  if (document.images) {
    document[imgName].src = eval(imgName+'1.src');
  }
}