function openModalWindowCenterred(url, width, height)
{
    var left = ((screen.availWidth/2)  - (width/2));
    var top  = ((screen.availHeight/2) - (height/2));
    var modalWindowFeatures = "width=" + width + ",height=" +
                    height + ",status.resizable.left=" + left + ",top=" +
                    top + ",screenX=" + left + ",screenY=" + top;
    myModalOpenWindow = window.open(url, "subWind", modalWindowFeatures);
    myModalOpenWindow.focus();
}