[zip]

всем спасибо \= решение найдено:

<script type="text/javascript">
<!--
  function toggle(switchElement) {
  var sex = document.getElementById('sex');
  var birthday = document.getElementById('birthday');
    if (switchElement.value == 'sex') {
      sex.style.display = '';
      birthday.style.display = 'none';
    }
    else if (switchElement.value == 'birthday') {
      sex.style.display = 'none';
      birthday.style.display = '';
    }
	else if (switchElement.value != 'birthday' && switchElement.value != 'sex') {
      sex.style.display = 'none';
      birthday.style.display = 'none';
    }
  }
-->
</script>
<form method="POST" name = "mainform" action="" class="text">
<table border="1">
	<tr>
		<td>#1</td>
		<td>#2</td>
	</tr>
	<tr>
		<td>
			<select name="select_left" multiple="multiple" size="15" style="width:200;" id="select_left_id" onChange="toggle(this);">
				<option value="passport_serie">Паспорт - Серия</option>
				<option value="passport_number">Паспорт - Номер</option>
				<option value="whom_issue">Паспорт - Кем выдан</option>
				<option value="when_issue">Паспорт - Когда выдан</option>
				<option value="sex" onClick="toggle(this);">Пол</option>
				<option value="birthday" onClick="toggle(this);">Дата рождения</option>
			</select>
		</td>
		<td border="1" style="width:100;" id="sex" style="display: none">
			<input type="checkbox" name="sex" value="0">муж<br />
			<input type="checkbox" name="sex" value="1">жен<br />
			<input type="checkbox" name="sex" value="2" checked>н/д<br />
		</td>
		<td border="1" style="width:100;" id="birthday" style="display: none">
			<p>от<input type="text" name="birthday" value="">
			до<input type="text" name="birthday" value=""></p>
			<input type="checkbox" name="birthday" value="2" checked>н/д<br />
		</td>
	</tr>
</table>
<p align="right">
    <input type = "submit" name = "generate" value="Отправить" style="font-weight:bold;">
</p>
</form>