codice:
  <html>

    <head>
      <script type="text/javascript" language="JavaScript">
      <!--

        function populateSelect( __hForm, __dwChoice )
        {
          if ( __dwChoice == 1 ) {
            with ( __hForm.elements["choice"] )
            {
              options.length          = 0;
              options[options.length] = new Option( "Testo #1", "Valore_1", false, false );
              options[options.length] = new Option( "Testo #2", "Valore_2", false, false );
              options[options.length] = new Option( "Testo #3", "Valore_3", false, false );
            }
          }

          else if ( __dwChoice == 2 ) {
            with ( __hForm.elements["choice"] )
            {
              options.length          = 0;
              options[options.length] = new Option( "Testo #4", "Valore_4", false, false );
              options[options.length] = new Option( "Testo #5", "Valore_5", false, false );
              options[options.length] = new Option( "Testo #6", "Valore_6", false, false );
            }
          }
        }

      //-->
      </script>
    </head>

    <body>

      <form>
        <input type="radio" name="defRadio" onclick="populateSelect( this.form, 1 );" /> Radio #1 #2 #3

        <input type="radio" name="defRadio" onclick="populateSelect( this.form, 2 );" /> Radio #4 #5 #6


        



        Selezioni disponibili: <select name="choice"></select>
      </form>

    </body>

  </html>