ciao a tutti,
ho un form con 10 campi:

cognome (obbligatorio)
nome (obbligatorio)
indirizzo
citta
provincia
telefono
fax
mail (obbligatorio)
oggetto
messaggio

e due radiobutton per la legge sulla privacy con SI e NO

come posso controllare all'invio del form che i campi siano compilati correttamente e che il radiobutton sia su SI?

vi mostro l'html

codice:
<form name="form" form style="margin:0;margin-top:23px" method="post" action="mail_success.php">
<table width="401" border="0" align="center">
<tr>
<td colspan="2"><div align="left">Cognome</div></td>
<td><input name="cognome" type="text" class="style-b" id="cognome" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
<span class="Stile2">*</span></td>
</tr>
<tr>
<td colspan="2"><div align="left">Nome</div></td>
<td><input name="nome" type="text" class="style-b" id="nome" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
<span class="Stile2">*</span></td>
</tr>
<tr>
<td colspan="2"><div align="left">Indirizzo</div></td>
<td><input name="indirizzo" type="text" class="style-b" id="indirizzo" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
</td>
</tr>
<tr>
<td colspan="2"><div align="left">Citt&agrave;</div></td>
<td><input name="citta" type="text" class="style-b" id="citta" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
</td>
</tr>
<tr>
<td colspan="2"><div align="left">Provincia</div></td>
<td><input name="provincia" type="text" class="style-b" id="provincia" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
</td>
</tr>
<tr>
<td colspan="2"><div align="left">Telefono</div></td>
<td><input name="telefono" type="text" class="style-b" id="telefono" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
</td>
</tr>
<tr>
<td colspan="2"><div align="left">Fax</div></td>
<td><input name="fax" type="text" class="style-b" id="fax" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
</td>
</tr>
<tr>
<td colspan="2"><div align="left">E-Mail</div></td>
<td><input name="mail" type="text" class="style-b" id="mail" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px">
<span class="Stile2">*</span></td>
</tr>
<tr>
<td colspan="3"><div align="left"></div></td>
</tr>
<tr>
<td colspan="3">Soggetto:</td>
</tr>
<tr>
<td colspan="3"><input name="oggetto" type="text" class="style-b" id="oggetto" style="width:213px;height:16px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px"></td>
</tr>
<tr>
<td colspan="3">Messaggio</td>
</tr>
<tr>
<td colspan="3"><textarea name="messaggio" cols="" rows="" class="style-b" id="messaggio" style="width:271px;height:75px;font-size:11px;border-color:#D4D4D4;border-style:solid;border-width:1px;overflow:auto;margin-bottom:17px;font-family:Arial"></textarea></td>
</tr>
<tr>
<td colspan="3">CONSENTI IL TRATTAMENTO DEI DATI<input name="radiobutton" type="radio" value="SI" checked>
  SI
  <input name="radiobutton" type="radio" value="NO">NO(<span class="style-b">Leggi la normativa </span>) </td>
</tr>
<tr>
<td colspan="3" class="style-b"></td>
</tr>
<tr>
<td width="63"></td>
<td colspan="2"><div align="right">
<input type="image" src="../images/reset.jpg" align="absmiddle" width="33" height="11" border="0">
<input type="image" src="../images/invia.jpg" align="absmiddle" width="33" height="11" border="0">
</div></td>
</tr>
</table>


</p>
</form>
Grazie mille