Scusate....
sarà poca conoscenza della materia (sicuramente)
o demenza senile (troppo giovane)

ecco il codice:
Cosa c'e che non va????

<HTML>
<HEAD>
<TITLE>modulo</TITLE>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
</HEAD>
<script>
function controlla(f) {
if (!form1.acc[0].checked ){
alert("Devi Autorizzare il trattamento dei dati personali")
return false
}
}

</script>

<BODY BGCOLOR=#FFFFFF text="#333333">
</p>
<table border="0" cellpadding="0" cellspacing="0" width="40%" align="center">
<tr>
<td width="100%">
<form method="post" name="form1" onsubmit=return"controlla(this);" action="formcdosys.asp">
<table width="423" border="0" cellspacing="0" cellpadding="0" style="border-collapse: collapse" bordercolor="#111111" height="251">
<tr>
<td width="77" height="15">
<font size="2" color="#333333">
Nome</font></td>
<td width="338" colspan="2" height="15">
<font color="#333333" size="2" face="Times New Roman">

<input type="text" name="nome" size="20"></font></td>
</tr>
<tr>
<td width="77" height="20">
<font size="2" color="#333333">
Cognome</font></td>
<td width="338" colspan="2" height="20">
<font color="#333333" size="2" face="Times New Roman">

<input type="text" name="cognome" size="20"></font></td>
</tr>
<tr>
<td width="77" height="20">
<font size="2" color="#333333">Via</font></td>
<td width="338" colspan="2" height="20">
<font face="Times New Roman" size="2" color="#333333">

<input name="via" type="text" id="altro" size="20"></font></td>
</tr>
<tr>
<td width="77" height="20"><strong style="font-weight: 400">
<font size="2">Città</font>[/b]</td>
<td width="338" colspan="2" height="20">
<font color="#333333" size="2" face="Times New Roman">

<input type="text" name="città" size="20"></font></td>
</tr>
<tr>
<td width="77" height="20"><strong style="font-weight: 400">
<font size="2">Provincia</font>[/b]</td>
<td width="338" colspan="2" height="20">

<font face="Times New Roman">
<select name="select">
<option value="numero1">opzione01</option>
<option value="numero1">opzione02</option>
<option selected>scegli opzione</option>
</select></font></td>
</tr>
<tr>
<td width="77" height="20"><strong style="font-weight: 400">
<font size="2" color="#333333">
Telefono</font>[/b]</td>
<td width="338" colspan="2" height="20">
<font color="#333333" size="2" face="Times New Roman">

<input type="text" name="tel" size="20"></font></td>
</tr>
<tr>
<td width="77" height="20"><strong style="font-weight: 400">
<font size="2" color="#333333">
E-mail</font>[/b]</td>
<td width="338" colspan="2" height="20">
<font color="#333333" size="2" face="Times New Roman">

<input type="text" name="email" size="20"></font></td>
</tr>
<tr>
<td width="77" height="82"><strong style="font-weight: 400">
<font size="2" color="#333333">
Messaggio</font>[/b]</td>
<td width="338" colspan="2" height="82">

<font size="1" color="#333333" face="Times New Roman">
<textarea name="messaggio" rows="5" cols="33" wrap="VIRTUAL"></textarea>
</font>

</td>
</tr>
<tr>
<td width="77" height="1">
<p align="center"><strong style="font-weight: 400">
<font style="font-size: 7pt">


</font>[/b]</td>
<td width="105" height="1">
<p align="center"><strong style="font-weight: 400">
<font style="font-size: 7pt">
Legge sulla Privacy</font>[/b]</td>
<td width="229" height="1">

<font face="Times New Roman">
<input type=radio value="si" name="acc" checked></font> Accetto

<font face="Times New Roman">
<input type=radio value="no" name="acc"></font> Rifiuto</td>
</tr>
</table>
<p align="center">
<font size="1" color="#333333" face="Verdana, Arial, Helvetica, sans-serif">
<input type="submit" name="Submit" value=" Invia " style="border-style: solid; border-width: 1"></font></p>
</form>
</td>
</tr>
</table>
</BODY>
</HTML>