Salve a tutti ho una pagina con un form mail, e voglio fare un controllo per sapere se i campi nome cognome ed email sono stati riempiti!
come faccio?

questo è il codice:

<html>
<head>
<title>Modulo Registrazione</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">

<script language="JavaScript">
<!--
function MM_openBrWindow(theURL,winName,features) { //v2.0
window.open(theURL,winName,features);
}
//-->
</script>
<style fprolloverstyle>A:hover {color: #FF9900}
</style>
</head>

<body bgcolor="#EFEFF5" link="#015E80" vlink="#015E80" alink="#015E80">
<div id="Layer1" style="position:absolute; left:5; top:14; width:553; height:332; z-index:1">
<form method="POST" action="mailto: m.manfre1@tin.it" name="info" onSubmit=""
<table width="550" border="0" cellspacing="0" cellpadding="0" style="border-collapse: collapse" bordercolor="#111111">
<tr>
<td colspan="2">
<table width="550" border="0" cellspacing="0" cellpadding="2" style="border-collapse: collapse" bordercolor="#111111" height="81">
<tr align="center">
<td colspan="5" width="565" height="17" bgcolor="#EFEFF5">

<font color="#474790" face="Verdana" size="2">Lascia qui sotto i
tuoi dati e riceverai presto risposta alla tua richiesta</font></td>
</tr>
<tr align="center">
<td colspan="5" width="565" height="1">
<p style="MARGIN: 0px 0px 0px 3px; LINE-HEIGHT: 100%">
<font face="Verdana" size="1">I campi con (*)
sono obbligatori</font></td>
</tr>
<tr>
<td width="105" height="31">
<div align="right" class="voci_form">
<font face="Verdana" size="2">* Cognome</font></div>
</td>
<td align="right" valign="middle" width="183" height="31">
<font face="Arial">
<input type="text" name="COGNOME" size="25"></font></td>
<td width="13" height="31"></td>
<td width="183" align="left" valign="middle" height="31">
<font face="Arial">
<input type="text" name="NOME" size="25"></font></td>
<td width="66" height="31">
<div align="left" class="voci_form">
<font face="Verdana" size="2">Nome *</font></div>
</td>
</tr>
<tr>
<td width="105" height="26">
<div align="right" class="voci_form">
<font face="Verdana" size="2">Indirizzo</font></div>
</td>
<td align="right" valign="middle" width="183" height="26">
<font face="Arial">
<input type="text" name="INDIRIZZO" size="25"><font size="2">
</font> </font>
</td>
<td width="13" height="26"></td>
<td align="left" valign="middle" width="183" height="26">
<font face="Arial">
<input type="text" name="LOCALITA'" size="25"><font size="2">
</font> </font>
</td>
<td width="66" class="voci_form" height="26">
<div align="left"><font face="Verdana" size="2">Localit&agrave;</font></div>
</td>
</tr>
<tr>
<td width="105" class="voci_form" height="31">
<div align="right"><font face="Verdana" size="2">Azienda</font></div>
</td>
<td align="right" valign="middle" width="183" height="31">
<font face="Arial">
<input type="text" name="AZIENDA" size="25"><font size="2">
</font> </font>
</td>
<td width="13" height="31"></td>
<td align="left" valign="middle" width="183" height="31">
<font face="Arial">
<input type="text" name="formmail_da" size="25"><font size="2">
</font>
</font>
</td>
<td width="66" class="voci_form" height="31">
<div align="left"><font face="Verdana" size="2">E-mail *</font></div>
</td>
</tr>
<tr>
<td width="105" class="voci_form" height="31">
<div align="right"><font face="Verdana" size="2">Telefono</font></div>
</td>
<td align="right" valign="middle" width="183" height="31">
<font face="Arial">
<input type="text" name="TELEFONO" size="25"><font size="2">
</font> </font>
</td>
<td width="13" height="31"></td>
<td align="left" valign="middle" width="183" height="31">
<font face="Arial">
<input type="text" name="FAX" size="25"><font size="2"> </font> </font>
</td>
<td width="66" class="voci_form" height="31">
<div align="left"><font face="Verdana" size="2">Fax</font></div>
</td>
</tr>
</table>
</td>
</tr>
<tr>
<td colspan="2">
<table width="553" border="0" cellspacing="0" cellpadding="0" style="border-collapse: collapse" bordercolor="#111111">
<tr>
<td width="98">
<div align="right" class="voci_form">
<font face="Verdana" size="2">Commenti</font></div>
</td>
<td align="center" valign="middle" width="386">
<font face="Arial">
<textarea name="RICHIESTA" cols="43" rows="4"></textarea><font size="2">
</font> </font>
</td>
<td width="69"></td>
</tr>
</table>
</td>
</tr>
<tr>
<td colspan="2">
<table width="550" border="0" cellspacing="0" cellpadding="0" style="border-collapse: collapse" bordercolor="#111111">
<tr>
<td valign="middle" width="250">
<div align="right"><font face="Verdana" size="1">
<a onClick="MM_openBrWindow('legge675.htm','','scroll bars=yes,width=430,height=400')" href="#">
<font color="#474790">Nota informativa ex legge 675/96</font></a></font></div>
</td>
<td width="40" align="center" valign="middle">
<font face="Arial">
<input type="checkbox" name="formmail_checkbox" value="checkbox" checked>
</font>
</td>
<td width="20" height="35"></td>
<td width="40" align="center" valign="middle">
<font face="Arial">
<input type="checkbox" name="formmail_checkbox2" value="checkbox">
</font>
</td>
<td width="250"><font face="Verdana" size="1" color="#474790">Non
desidero essere informato

su eventuali nuove iniziative commerciali</font></td>
</tr>
</table>
</td>
</tr>
<tr>
<td valign="middle" align="center">
<font face="Arial">
<input type="submit" name="formmail_Submit" value=" Invia " style="color: #FFFFFF; font-weight: bold; background-color: #474790">
</font>
</td>
<td height="30" align="center" valign="middle">
<font face="Arial">
<input type="reset" name="formmail_reset" value=" Cancella " style="color: #FFFFFF; font-weight: bold; background-color: #474790">
</font>
</td>
</tr>
</table>
<font face="Arial">
<input type="hidden" name="formmail_paginako" value="/pro/princ_file/errore.html">
</font
<font face="Arial">
<input type="hidden" name="formmail_oggetto" value="Richiesta Registrazione">
</font <font face="Arial">
<input type="hidden" name="formmail_paginaok" value="/pro/princ_file/conferma.html">
</font>
<font face="Arial">
<input type="hidden" name="formmail_a" value="m.manfre1@tin.it">
</font </form>
</div>
</body>
</html>

ringrazio anticipatamente.