function nav_sw(daImage, daSrc){
  
 var picURL = "/img/";
  
  var objStr,obj;
   if(document.images){
  	if (typeof(daImage) == 'string'){
  	 objStr = 'document.' + daImage;
  	 obj = eval(objStr);
  	 obj.src = picURL+daSrc;
     }else if ((typeof(daImage) == 'object') && daImage && daImage.src){
    		daImage.src = picURL+daSrc;
      }
    }
   }