if (document.images) {            
            img1on = new Image();   img1on.src = "images/b1a.gif"; 
            img2on = new Image();   img2on.src = "images/b2a.gif";
            img3on = new Image();   img3on.src = "images/b3a.gif";  
            img4on = new Image();   img4on.src = "images/b4a.gif";  
            img5on = new Image();   img5on.src = "images/b5a.gif";
            img6on = new Image();   img6on.src = "images/b6a.gif";
            img7on = new Image();   img7on.src = "images/b7a.gif";
            

            img1off = new Image();  img1off.src = "images/b1.gif";
            img2off = new Image();  img2off.src = "images/b2.gif";
            img3off = new Image();  img3off.src = "images/b3.gif";
            img4off = new Image();  img4off.src = "images/b4.gif";
            img5off = new Image();  img5off.src = "images/b5.gif";
            img6off = new Image();  img6off.src = "images/b6.gif";
            img7off = new Image();  img7off.src = "images/b7.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");        
            }
    }