ecco la funzione:

codice:
<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>
la chiamata:

codice:
<input type="text" name="textfield" onKeyUp="Controllo(this.form);">
ciao