var isIMG = document.images;
var Arrowon;
var Arrowoff;

if (isIMG) {
   Arrowon = new Image(7,7);
   Arrowon.src = "arrow_over.jpg";
   Arrowoff = new Image(7,7);
   Arrowoff.src = "arrow_down.jpg";
}
function Arrow(Arrowname) {
   if (isIMG) {
     document[Arrowname].src = (document[Arrowname].src.indexOf('arrow_over.jpg') != -1) ? 'arrow_down.jpg' : 'arrow_over.jpg';

   }
}