Javascript: Select폼에서의 링크 이동

<form action="어쩌구" method="get">
<fieldset>
<p>
<legend>페이지 이동 폼</legend>
<label for="sel">페이지 선택</label>
<select name="sel" id="sel" tabindex="1">
<optgroup  label="링크들">
 <option value="http://naver.com">네이버</option>
 <option value="http://empas.com">엠파스</option>
 <option value="http://daum.net">다음</option>
</optgroup>
</select>
<input type="button" value="이동" onclick="document.location.href=sel.value" onkeypress="document.location.href=sel.value" tabindex="2" />
</p>
</fieldset>
</form>