da sistemare l'operer :master:
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>Pagina senza titolo</title>
<script language="javascript" type="text/javascript">
// <!CDATA[

function Button1_onclick() 
{
    var c = document.forms[0].ID_Utente;
    var s = "";
    for (var i = 0; i < c.length; i++)
        if(s == "")
            s = c[i].value;
        else
            s += "," + c[i].value;
    alert("tutti i valori: " + s);
    
    
    s = "";
    for (var i = 0; i < c.length; i++)
        if(c[i].checked)
            if(s == "")
                s = c[i].value;
            else
                s += "," + c[i].value;

    alert("tutti i valori selezionati: " + s);
    
}

// ]]>
</script>
</head>
<body>
<form action="?">
    <input type="checkbox" name="ID_Utente" value="1"/>
    <input type="checkbox" name="ID_Utente" value="2"/>
    <input type="checkbox" name="ID_Utente" value="3"/>
    <input id="Button1" type="button" value="button" onclick="return Button1_onclick()" />
</form>

</body>
</html>