<tr>
    <td class="tdLabel"><label for="cb" class="label">mylabel:</label></td>
    <td>
<script type="text/javascript">
	function autoPopulate_cb(targetElement) {
		targetElement.form.elements['foo'].value=targetElement.options[targetElement.selectedIndex].value;
	}
</script>
<input type="text" name="foo" value="hello" id="cb"/><br/>
<select onChange="autoPopulate_cb(this);">
    <option value="foo">foo</option>
    <option value="bar">bar</option>
    <option value="baz">baz</option>
</select>
    </td>
</tr>