ecco la pagina completa:

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Documento senza titolo</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">

<script language="JavaScript">

var no=new Array("0.0", "000", ".00", "00.", "...", "..0", "0..", ".0.");

function Controllo(f) {
 e=f.elements;
 for (i=0; i<e.length; i++)
  if (e[i].type=="text")
  for (j=0; j<no.length; j++)
   if (no[j]!=e[i].value) continue;
   else {
    f.nomesubmit.disabled=true;
    return;
   }
 f.nomesubmit.disabled=false;
}

</script>

</head>

<body>
<form name="f">
<input type="text" name="textfield" onKeyUp="Controllo(this.form);">


<input type="submit" name="nomesubmit" disabled value="Invia">
</form>
</body>
</html>
fammi sapere.