function fenster(winname,wintitel,breite,hoehe) {

var links=screen.width/2-breite/2;
var oben=screen.height/2-hoehe/2;
NewWin = window.open(winname, wintitel, "width="+breite+",height="+hoehe+",top="+oben+",left="+links+",toolbar=0,location=0,scrollbars=yes,resizable=yes");


}