function Go(url) {
    window.location.href = url;
}

(function($) {
    var cache = [];
    // Arguments are image paths relative to the current page.
    $.preLoadImages = function() {
        var args_len = arguments.length;
        for (var i = args_len; i--; ) {
            var cacheImage = document.createElement('img');
            cacheImage.src = arguments[i];
            cache.push(cacheImage);
        }
    }
})(jQuery)

$(function() {
$("#MainMenu img").each(function() {  LoadAltFile(this); })
    .mouseenter(function() { $(this).attr('src', $(this).attr('srcalt')); })
    .mouseleave(function() { $(this).attr('src', $(this).attr('srcnorm')); });
});

function LoadAltFile(img) {
    var src = $(img).attr('src');

    var filename = src.substring(0, src.lastIndexOf("."));
    var extension = src.substring(src.lastIndexOf("."));

    var srcalt = filename + "_on" + extension;
    $(img).attr('srcalt', srcalt);
    $(img).attr('srcnorm', src);

    $.preLoadImages(srcalt);
}