function window_open(url,target,W,H)
 {
    var X = (screen.width/2)-(W/2);
    var Y = (screen.height/2)-(H/2);

    var winPref = "width=" + W + ",height=" + H
                + ",innerWidth=" + W + ",innerHeight=" + H
                + ",left=" + X + ",top=" + Y
                + ",screenX=" + X + ",screenY=" + Y
                + ",dependent=yes,titlebar=no,scrollbars=no,resizable=no";


    window_open.popup = window.open( url, target, winPref );
    window_open.popup.resizeTo(1*W,1*H);
    window_open.popup.focus();
 }