Please help me with this easy plugin

This is the code, i have added only the last filter for add a custom order of posts…..but with my addition the plugin doesn’t work…

<?php
/*
Plugin Name: Custom Home
Plugin URI: http://wordpress.org/support/topic/93438
Description: Display only those posts on your home page with a specific custom field key (and optional value).
Author: Kaf Oseo
Version: R1.0.1
Author URI: http://szub.net

	Copyright (c) 2006 Kaf Oseo (http://szub.net)
	Custom Home is released under the GNU General Public License
	(GPL) http://www.gnu.org/licenses/gpl.txt

	This is a WordPress 2 plugin (http://wordpress.org).

Usage:
Make sure to edit the $key and $value variables found within the
szub_custom_home_where() function below for the custom field key
and value to match on. Leaving the $value var empty will cause a
match on custom key only.

~Changelog:
R1.0.1 (Nov-09-2006)
A little fix to the 'where' and 'join' hookups.
*/

function szub_custom_home_where($where) {
/* >> Begin user-configurable variables >> */
//  $key - Custom key to match. Modify to your needs.
	$key = 'voto';

//  $value - Custom value to match. Leave empty if you must only match $key.
	$value = '';
/* << End user-configurable variables << */

	if( is_category() ) {
		global $wpdb;

		$where .= " AND $wpdb->postmeta.meta_key = '$key' ";

		if( $value )
			$where .= " AND $wpdb->postmeta.meta_value = '$value' ";
	}

	return $where;
}

function szub_custom_home_join($join) {
	global $wpdb;

	if( is_category() ) {
		$join .= " LEFT JOIN $wpdb->postmeta ON $wpdb->posts.ID = $wpdb->postmeta.post_id ";
	}

	return $join;
}

function szub_custom_home_orderby($orderby) {
	global $wpdb;

	if( is_category() ) {
		$orderby .= " $wpdb->postmeta.meta_value ASC ";
	}

	return $orderby;
}

add_filter('posts_where', 'szub_custom_home_where');
add_filter('posts_join', 'szub_custom_home_join');
add_filter('posts_orderby', 'szub_custom_home_orderby');
?>