var loc="fileadmin/images/nav_top/";
 var sfx=".gif";
 
 function swap(PicName1,DatName1,PicName2,DatName2){
  window.document.images[PicName1].src = loc+DatName1+sfx;
  window.document.images[PicName2].src = loc+DatName2+sfx;
}

 function swapone(PicName,DatName){
  window.document.images[PicName].src = loc+DatName+sfx;
}