codice:
<head>
<script language="javascript">
function disabilita() {
document.aaa.mmm.disabled=true;
}

</script>
</head>
<body>

<form name="aaa" >
  <input type="submit" value="Invia" name="mmm" onclick="javascript:disabilita()">
  <input type="reset" value="Reimposta" name="B2"></p>
</form>