<form action="xxx.cgi">
<select name="categori">
<optgroup label="カテゴリ">
<option value="HTML">HTML
<option value="CSS">CSS
<option value="XML" selected>XML
</optgroup>
</select>

<select name="categori2" size="3" multiple>
<option value="HTML">HTML
<option value="CSS">CSS
<option value="XML">XML
</select>
</form>