function popup(obj, W, H, wtype) {
    if (document.all) {
        var xMax = screen.width, yMax = screen.height;
    } else {
        if (document.layers) {
            var xMax = window.outerWidth, yMax = window.outerHeight;
        } else {
            var xMax = 640, yMax = 480;
        }
    }
    var xOffset = (xMax - W) / 2, yOffset = (yMax - H) / 2;
    open(obj.href + '&single_module=1', wtype, "location=no,scrollbars=yes,width=" + W + ",height=" + H + ",top=" + yOffset + ",left=" + xOffset);
    return false;
}