function popup(url) {	
    if (screen.height && navigator.appName != 'Opera')  {
        X = screen.width;
        Y = screen.height;
    } else if (document.body && document.body.offsetHeight) {
        X = document.body.offsetWidth;
        Y = document.body.offsetHeight;
    } else if (window.innerHeight) {
        X = window.innerWidth;
        Y = window.innerHeight;
    } else { 
        X = 600;
        Y = 600;
    }	
	X = (X - 680 ) / 2;
	Y = (Y - 500 ) / 2;
	var Win = window.open( url, 'help', 'width=680,height=500,top='+Y+',left='+X+',resizable=1,scrollbars=0,location=no,directories=no,status=no,menubar=no,toolbar=no');
	Win.focus();
 }