function popup(url, larghFin, lunghFin) { 
var scw = screen.width; 
var sch = screen.height; 
var dasx= Math.round((scw-larghFin)/2); 
var datop = Math.round((sch-lunghFin)/2); 
var parametri = "scrollbars=0,width="+larghFin+",height="+lunghFin+",left="+dasx+",top="+datop; 
window.open(url, "", parametri); 
}