var cont=0;
function popup(nome) {
var w=600;
var h=500;
x=(screen.width-w)/2;
y=(screen.height-h)/2;
cont++;
window.open(nome,'pagina'+cont,'left='+ x +',top='+y+',width='+ w +',height='+ h +',resizable=yes,status=no,location=no,toolbar=no,scrollbars=yes');

}