if (document.images)   {
     image1on = new Image();
     image1on.src="/img/a2.jpg";

     image1off = new Image();
     image1off.src = "/img/a1.jpg";

}

if (document.images)   {
     image2on = new Image();
     image2on.src="/img/b2.jpg";

     image2off = new Image();
     image2off.src = "/img/b1.jpg";

}

if (document.images)   {
     image3on = new Image();
     image3on.src="/img/c2.jpg";

     image3off = new Image();
     image3off.src = "/img/c1.jpg";

}

if (document.images)   {
     image4on = new Image();
     image4on.src="/img/d2.jpg";

     image4off = new Image();
     image4off.src = "/img/d1.jpg";

}


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

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