function lightup(imgName) {
    if (document.images) {
        imgOn = "images/links/" + imgName + "_hover.jpg";
        document[imgName].src = imgOn;
    }
}

function turnoff(imgName) {
    if (document.images) {
        imgOff = "images/links/" + imgName + ".jpg";
        document[imgName].src = imgOff;
    }
}