function callback(){
	var mypage="callback.php";
	var w=300; var h=440;
	var winbreite=(screen.width-w)/10;
	var winhoehe=(screen.height-h)/10;
	var myname="callback";
	winprops='height='+h+',width='+w+',top='+winhoehe+',left='+winbreite+',scrollbars=1,resizable=0';
	win=window.open(mypage, myname, winprops);
	win.focus();
}