function preloadImg(imgSrc) {
    var tmpImg = new Image();
    tmpImg.src = imgSrc;
}

function chgImg(elmId, imgSrc, w, h) {
    if (!document.all && document.getElementById) {
        var img = document.getElementById(elmId);
        img.src = imgSrc;
    } else if (document.all) {
        var img = document.all[elmId];
        img.src = imgSrc;
    }
}