function popup(url)
{

var breite = 800;
var hoehe = 523;

var links = (screen.width-breite)/2;
var oben = (screen.height-hoehe)/2;

Fenster = window.open(url, "popup", "width="+breite+", height="+hoehe+", left="+links+", top="+oben+", toolbar=no,location=no, directories=no, status=no, menubar=no, scrollbars=yes, resizable=no");
Fenster.focus();
}