function popup (url) {
 var nwl = (screen.width-750)/2;
 var nwh = (screen.height-550)/2;
 fenster = window.open(url, "pop", 'width=750,height=550,resizable=yes,scrollbars=yes,left='+nwl+',top='+nwh+'');
 fenster.focus();
 return false;
}
function hintpopup() {
document.write("<br \/>[opens pop-up window]");
}