function openPopup (url) {

 var width =901;
 var height = 600;
 var l = (screen.availWidth - width) / 2;
 var t = (screen.availHeight - height) / 2;
 
 var popup = window.open(url,"mediaSpace","width=" + width +
                                            ",height=" + height +
                                            ",left=" + l +
                                            ",top=" + t + ",resizable=no;");

 popup.focus();
}