Widget sample with tinymce wysiwyg editor

custom-widget.php

<?php
class Custom_Widget extends WP_Widget {
	function Custom_Widget() {
		...
	}
	
	function widget($args, $instance) {
		...
	}
	
	function update($new_instance, $old_instance) {
		$instance = $old_instance;
		$instance['title'] = strip_tags($new_instance['title']);
		if ( isset($new_instance['description']) ) {
			if ( current_user_can('unfiltered_html') ) {
				$instance['description'] = $new_instance['description'];
			} else {
				$instance['description'] = wp_filter_post_kses($new_instance['description']);
			}
		}
		
		return $instance;
	}
	
	function form($instance) {
		$defaults = array(
			'title' => 'RECOMMENDED READING',
			'description' => '<p>Available for <u>Immediate</u> Download</p>'
		);
		$instance = wp_parse_args( (array) $instance, $defaults );
		
		$title = esc_attr($instance['title']);
		$description = $instance['description'];
?>
	<p>
		<label for="<?php echo $this->get_field_id('title'); ?>">
			<i><strong><?php _e( 'Title' ); ?></strong></i><br>
			<input class="widefat" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title'); ?>" type="text" value="<?php echo $title; ?>" />
		</label>
	</p>
	<p>
		<label for="<?php echo $this->get_field_id('description'); ?>">
			<i><strong><?php _e( 'Description' ); ?></strong></i>
		</label><br/>
		<textarea cols="53" rows="4" class="mceEditor" id="<?php echo $this->get_field_id('description'); ?>" name="<?php echo $this->get_field_name('description'); ?>"><?php echo $description; ?></textarea>
		<a href="#" onclick="showMCE('<?php echo $this->get_field_id('description'); ?>',this);return false;">Show WYSIWYG Editor</a>
	</p>
<?php
	}	
}

// add javascript to widgets page header
add_action('admin_head-widgets.php', 'custom_tinymce');
function custom_tinymce() {
	echo '<script type="text/javascript">
		<!--
		function showMCE(id,linkObj) {
			if (tinyMCE.getInstanceById(id) == null) {
				linkObj.innerHTML = "Hide WYSIWYG Editor";
				tinyMCE.mode = "specific_textareas";
				tinyMCE.execCommand("mceAddControl", false, id);
			}	else {
				linkObj.innerHTML = "Show WYSIWYG Editor";
				tinyMCE.execCommand("mceRemoveControl", false, id);
			}
		}
		
		tinyMCE.init({
		theme : "advanced",
		mode : "none",
		plugins : "style",
		skin: "default",
		dialog_type:"modal",
		theme_advanced_buttons1: "fontselect,fontsizeselect,formatselect,|,bullist,numlist,|,justifyleft,justifycenter,justifyright,justifyfull",
		theme_advanced_buttons2: "bold,italic,underline,strikethrough,|,forecolor,styleprops,|,link,unlink,|,removeformat,charmap,blockquote,|,outdent,indent,|,undo,redo",
		theme_advanced_buttons3: "",
		theme_advanced_buttons4: "",
		spellchecker_languages: "+English=en,Danish=da,Dutch=nl,Finnish=fi,French=fr,German=de,Italian=it,Polish=pl,Portuguese=pt,Spanish=es,Swedish=sv",
		theme_advanced_toolbar_location:"bottom",
		theme_advanced_toolbar_align:"center",
		theme_advanced_resizing:"1",
		theme_advanced_resize_horizontal:"",
		editor_selector: "mceEditor",
		width : "200",
		height : "200",
		setup : function(ed){ed.onChange.add(function(ed){tinyMCE.triggerSave();});}
		});
		-->
		</script>
	';
}
?>

What exactly do I need to do in order to install this code? I really need to get the tinyMCE functionality for my widgets. Please help!