Azz...forse ho capito male
Codice PHP:
<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function updateSum()
{
document.form1.Totale.value = parseInt(document.form1.a.value) +
parseInt(document.form1.b.value) + parseInt(document.form1.c.value);
}
//-->
</script>
</head>
<body>
<form action="xxx.php" method="post" name="form1" id="form1">
A <input type="text" name="a" value="0" onChange="updateSum();" /><br />
B <input type="text" name="b" value="0" onChange="updateSum();" /><br />
C <input type="text" name="c" value="0" onChange="updateSum();" /><br />
Totale <input type="text" name="Totale" value="0" readonly>
</form>
</body>
</html>