Frontpage Filter Problem, Plugin richtig?!

<?php
 /*
Plugin Name: Front Page Filter
Plugin URI: http://smallestbusiness.com/category/wordpress
Description: A plugin that filters categories for the main page.
Author: Ami Heines
Version: 0.9
Author URI: http://smallestbusiness.com
 */
  /*  Copyright 2006  Ami Heines  (email form : http://smallestbusiness.com/about)


    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.


    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.


    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
?>
<?php
add_option('sb_front_page_filter', '= 1', 'filter posts by category. example:"=1" to show only posts from category 1\n another example: "!=2"', 'yes');


function sb_filter_add_option_page() {
  if (function_exists('add_options_page')) {
    add_options_page('Front Page Filter', 'Front Page Filter', 9, basename(__FILE__), 'sb_fpf_options_subpanel');
  }
}


function sb_fpf_options_subpanel() {
  if($_POST['sb_fpf_save']){
    update_option('sb_front_page_filter',$_POST['sb_front_page_filter']);
    echo '<div class="updated"><p>Front Page Category Filter saved successfully.</p></div>';
  }


        ?>
        <div class="wrap">
        <h2>Front Page Category Filter Options</h2>
        <form method="post" id="sb_fpf_options">
                <fieldset class="options">
                <legend>Category Filter for Main Page</legend>
                <table width="100%" cellspacing="2" cellpadding="5" class="editform">
                        <tr valign="top">
       <th width="33%" scope="row">Filter:</th>
                                <td><input name="sb_front_page_filter" type="text" id="sb_front_page_filter"
       value="<?php echo get_option('sb_front_page_filter') ;?>" size="30" maxlength="80" />
       <br />Sets the category filter for the main page of the website.
</td>
                        </tr>
                </table>
    <h2>Help</h2>
                           If you need help, go to the <a href="http://smallestbusiness.com/category/wordpress">suport area</a> for this plugin.
                <p class="submit"><input type="submit" name="sb_fpf_save" value="Save" /></p>
                </fieldset>
        </form>
        </div>
        <?php
}


function sb_filter_category_where($where) {
  if (is_home()) {
    $where .= " AND category_id " . get_option('sb_front_page_filter');
  }
  return $where;
}


function sb_filter_category_join($join) {
  global $table_prefix;
  //echo $table_prefix;
  if (is_home()) {
    $join .= " LEFT JOIN ".$table_prefix."post2cat ON (".$table_prefix."posts.ID = ".$table_prefix."post2cat.post_id)";
  }
  return $join;
}


add_filter('posts_where', 'sb_filter_category_where');
add_filter('posts_join' , 'sb_filter_category_join');
add_action('admin_menu' , 'sb_filter_add_option_page');


?>