function open_popup(op_url, op_width, op_heigth) {
	//Imposto i parametri secondo le specifiche di http://www.w3schools.com/HTMLDOM/met_win_open.asp

	var op_options = 'channelmode=0';
	op_options += ',directories=0';
	op_options += ',fullscreen=0';
	op_options += ',height=' + op_heigth;
	op_options += ',left=' + Math.floor((screen.width - op_width) / 2);
	op_options += ',location=0';
	op_options += ',menubar=0';
	op_options += ',resizable=0';
	op_options += ',scrollbars=0';
	op_options += ',status=0';
	op_options += ',titlebar=0';
	op_options += ',toolbar=0';
	op_options += ',top=' + Math.floor((screen.height - op_heigth) / 2);
	op_options += ',width=' + op_width;

	site = open(op_url, '_blank', op_options);
	return false;
}