function openCenterWindow(url, width, height, options)
{
    var left = parseInt((screen.availWidth/2) - (width/2));
    var top = parseInt((screen.availHeight/2) - (height/2));
    var windowFeatures = "width=" + width + ",height=" + height + "," + options + ",left=" + left + ",top=" + top + "screenX=" + left + ",screenY=" + top;

    return window.open(url, "", windowFeatures);   
}