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></title>

    <script language="javascript" type="text/javascript">
// <!CDATA[
function table_onclick(e, v) 
{
    if (!e) var e = window.event;
    var target = (e.target) ? e.target : e.srcElement;
    if(target.tagName.toLowerCase() == "input" && target.type.toLowerCase() == "checkbox")
    {
        var elementi = v.getElementsByTagName("INPUT");
        var n = elementi.length;
        var punteggio = 0;
        for(var i = 0; i < n; i++)
        {
            var elemento = elementi[i];
            if( (elemento.type != undefined && elemento.type.toLowerCase() == "checkbox" ) )
            {
                if(elemento.checked) punteggio += parseInt(elemento.value);
            }
        }
        document.getElementById("somma").value = punteggio; 
    }
   
}


// ]]>
</script>

</head>
<body>
    <table onclick="table_onclick(event, this);">
        <tr>
            <td colspan="4">
                gioco
            </td>
        </tr>
        <tr>
            <td colspan="2">
                Interessi
            </td>
            <td colspan="2">
                Sport
            </td>
        </tr>
        <tr>
            <td>
                Internet
            </td>
            <td>
                <input type="checkbox" name="interessi" value="1" />
            </td>
            <td>
                Calcio
            </td>
            <td>
                <input type="checkbox" name="sport" value="1" />
            </td>
        </tr>
        <tr>
            <td>
                Computer
            </td>
            <td>
                <input type="checkbox" name="interessi" value="2" />
            </td>
            <td>
                Tennis
            </td>
            <td>
                <input type="checkbox" name="sport" value="2" />
            </td>
        </tr>
        <tr>
            <td>
                Libri
            </td>
            <td>
                <input type="checkbox" name="interessi" value="3" />
            </td>
            <td>
                Basket
            </td>
            <td>
                <input type="checkbox" name="sport" value="3" />
            </td>
        </tr>
        <tr>
            <td colspan="2">
                Punteggio
            </td>
            <td colspan="2">
                <input id="somma" name="somma" type="text" size="10" />
            </td>
        </tr>
    </table>
</body>
</html>