Una cosa del genere:
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<script type="text/javascript">
<!-- //
function aggiungi(opt){
if(opt == "Titolo")
document.getElementById("lingua").options[2] = new Option("ESP");
else
document.getElementById("lingua").removeChild(document.getElementById("lingua").options[2]);
}
// -->
</script>
</head>
<body>
<form action="" method="post" name="f1">
  <select name="prima" id="prima" onchange="aggiungi(this.options[this.selectedIndex].value)">
    <option value="Numero">Numero</option>
    <option value="Data">Data</option>
    <option value="Titolo">Titolo</option>
  </select>
  <select name="lingua" id="lingua">
    <option value="ITA">ITA</option>
    <option value="ENG">ENG</option>
  </select>
</form>
</body>
</html>