Create Search Field for Custom Field or Attribute

Thanks for tip. If I only wanted to be able to search for tags (text box search not drop down) what would I have to modify to be able to add this to the search form.

add_action('em_template_events_search_form_ddm', 'my_em_styles_search_form');
function my_em_styles_search_form(){
	$my_em_styles = (is_array(get_option('my_em_styles'))) ? get_option('my_em_styles'):array();
	?>
	<!-- START Styles Search -->
	<select name="style">
		<option value=''>All Styles</option>
		<?php foreach($my_em_styles as $style_id=>$style_name): ?>
		 <option value="<?php echo $style_id; ?>" <?php echo ($_POST['style'] == $style_id) ? 'selected="selected"':''; ?>><?php echo $style_name; ?></option>
		<?php endforeach; ?>
	</select>
	<!-- END Styles Search -->
	<?php
}