scusa
ecco il codice :

questo e lo script

<script language="javascript">
function control(){
var espressione= /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-]{2,})+\.)+([a-zA-Z0-9]{2,})+$/;
with(document.dati){
if(Fname.value == ""){
alert("inserire nome")
Fname.focus()
return false
}
if(Lname.value == ""){
alert("inserire cognome")
Lname.focus()
return false
}
if(mail.value == ""){
alert("inserire email")
mail.focus()
return false
}
if(!espressione.test(mail.value)){
alert("mail non valida")
return false
}
}

return true
}
</script>




questo e il form:


<form name="dati" action="http://secnet.di.unito.it/cgi-bin/parrot.cgi" onSubmit="return control();" method="post" >

<fieldset class="cent">
<legend> User Details </legend>

<table border="0" cellspacing="30">
<tr>
<td> First name: </td>
<td> <input type="text" name="Fname" /> </td>
</tr>
<tr>
<td> Last name: </td>
<td> <input type="text" name="Lname" /> </td>
</tr>
<tr>
<td> E-mail: </td>
<td> <input type="text" name="mail" /> </td>
</tr>
</table>

</fieldset>