Allora questo fa ciò che ti serve

codice:
<head>
<title>Pagina form multipli</title>

<script>
function $(id) {
  return document.getElementById(id);
}

function check(field) {
  return ($(field).value != '');
}
</script>

</head>
<body>


<form name="form1" method="POST" action="script_form1.asp" onsubmit="return check('campoT1');">
  

<input type="text" name="T1" id="campoT1" size="20"></p>
  

<input type="reset" value="cancella"><input type="submit" value="Invia"></p>
</form>


<form name="form2" method="POST" action="script_form2.asp" onsubmit="return check('campoT2');">
  

<input type="text" name="T2" id="campoT2"  size="20"></p>
  

<input type="reset" value="cancella"><input type="submit" value="Invia"></p>
</form>


<form name="form3" method="POST" action="script_form3.asp" onsubmit="return check('campoT3');">
  

<input type="text" name="T3" id="campoT3" size="20"></p>
  

<input type="reset" value="cancella"><input type="submit" value="Invia"></p>

</form>
</body>
</html>

Ciao