if (document.images) {
img1on = new Image();	
img1on.src = "images/tdd-03.jpg";
       
img1off = new Image();	
img1off.src = "images/tdd1.jpg";

}

       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");
        
                                }
       }