Originariamente inviato da badaze
Prova questo.

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function controlla(unValore) {
 ereg1 = /^tmp[0-9]{6}$/;
 ereg2 = /^[0-9]{8,11}$/;
 //
 if (unValore.match(ereg1)) {
  //-------- matches tmp + 6 figures
	//alert('ok - tmp');
	return true;
 } else {
  if (unValore.match(ereg2)) {
   //-------- matches from 8 to 11 figures
	 //alert('ok - 8-11');
	 return true; 
	} else {
	 //-------- doesnot match anything
   //alert('ko');
	 return false;
  } // if (unValore.match(ereg2))
 } // if (unValore.match(ereg1))
} // function controlla(unValore)

function controllaForm() {
 unValore = document.mioform.numero.value;
 if (controlla(unValore)) {
  //-------- controllo immissione
  if (unValore.substr(0,3) == 'tmp') {
	 document.mioform.cod.value = 'temp';
	} else {
 	 document.mioform.cod.value = 'valido';
	} // if (unValore.substr(0,3) == 'tmp')
	alert( document.mioform.cod.value);
	return true;
 } else {
  alert('Immissione scoretta\nImpossibile continuare');
  return false
 } // if (controlla(unValore)) 
} // function controllaForm()
//-->
</script>

</head>
<body>
<form name="mioform" method="post" onsubmit="return controllaForm()">
 Digitare :
 <input type="text" name="numero" size="13" maxlength="11">

 <input type="submit" value="Submit">
 <input type="hidden" name="cod"/>
</form>
</body>
</html>
Ti ringrazio...lo provo e poi ti faccio sapere!!!!