Here perhaps this code can bring you an idea how to use mutiply controls with indexes and how to catch the key event of your browser.
Code:
<html>
<head>
<title></title>

<script language=javascript>
<!--

function Continue_onclick() {

  for ( i=0; 0<rd.length; i++ ) {
    if ( rd[i].checked == true ) {
      alert ( 'You have selected ' + rd[i].value );
      break;
    }
  }

}

function document_onkeydown() {

  var sEnter = '13';
  if ( window.event.keyCode.toString() == sEnter ){
    alert ( 'You have pressed the Enter key!' );
  }

}

//-->
</script>

<script language=javascript for=document event=onkeydown>
<!--
 document_onkeydown()
//-->
</script>

</head>
<body>

<table id="oTable" name="oTable">
  <tr>
    <td>
    <input type="radio" id="rd" name="rd" value="Red" checked>Red<br>
    <input type="radio" id="rd" name="rd" value="Green">Green<br>
    <input type="radio" id="rd" name="rd" value="Blue">Blue<br>
    <input type="radio" id="rd" name="rd" value="Black">Black
    </td>
  </tr>
  <tr>
    <td>
    <input type="button" value="Button" id="Continue" name="Continue" LANGUAGE=javascript onclick="return Continue_onclick()">
    </td>
  </tr>
</table>

</body>
</html>