if(document.images) {

img1on = new Image ();
img1on.src = "images/zurueck_over.gif";
img2on = new Image ();
img2on.src = "images/weiter_over.gif";
img3on = new Image ();
img3on.src = "images/mehr_over.gif";

img1off = new Image ();
img1off.src = "images/zurueck.gif";
img2off = new Image ();
img2off.src = "images/weiter.gif";
img3off = new Image ();
img3off.src = "images/mehr.gif";
}

function imgOn(imgName) {
         if (document.images) {
            document[imgName].src = eval(imgName + "on.src");
         }
}

function imgOff(imgName) {
         if (document.images) {
            document[imgName].src = eval(imgName + "off.src");
         }
}