Wordpress - Remove Ability for Other Users to View Administrator in User List?

Hi @Carlos:

Try adding the following to your theme's functions.php file, or in a .php file within a plugin that you might be writing (which works for WordPress 3.1.x):

add_action('pre_user_query','yoursite_pre_user_query');
function yoursite_pre_user_query($user_search) {
  $user = wp_get_current_user();
  if ($user->ID!=1) { // Is not administrator, remove administrator
    global $wpdb;
    $user_search->query_where = str_replace('WHERE 1=1',
      "WHERE 1=1 AND {$wpdb->users}.ID<>1",$user_search->query_where);
  }
}

If you have WordPress 3.0.x try this instead (since WordPress didn't add the 'pre_user_query' hook until 3.1):

add_action('pre_user_search','yoursite_pre_user_search');
function yoursite_pre_user_search($user_search) {
  $user = wp_get_current_user();
  if ($user->ID!=1) { // Is not administrator, remove administrator
    global $wpdb;
    $user_search->query_where = str_replace('WHERE 1=1',
      "WHERE 1=1 AND {$wpdb->users}.ID<>1",$user_search->query_where);
  }
}

Here's a mod to MikeSchinkel's answer that checks if the current user has a role of administrator and if not it only selects users that are subscribers.

add_action('pre_user_query','yoursite_pre_user_query');
function yoursite_pre_user_query($user_search) {
    $user = wp_get_current_user();

    if ( $user->roles[0] != 'administrator' ) { 
        global $wpdb;

        $user_search->query_where = 
        str_replace('WHERE 1=1', 
            "WHERE 1=1 AND {$wpdb->users}.ID IN (
                 SELECT {$wpdb->usermeta}.user_id FROM $wpdb->usermeta 
                    WHERE {$wpdb->usermeta}.meta_key = '{$wpdb->prefix}user_level' 
                    AND {$wpdb->usermeta}.meta_value = 0)", 
            $user_search->query_where
        );

    }
}

User Levels are deprecated, so this method checks against capabilities instead:

/** Hide Administrator From User List **/
function isa_pre_user_query( $user_search ) {
    if ( !current_user_can( 'administrator' ) ) { // Is Not Administrator - Remove Administrator
        global $wpdb;

        $user_search->query_where = str_replace(
            'WHERE 1=1', 
            "WHERE 1=1 AND {$wpdb->users}.ID IN (
              SELECT {$wpdb->usermeta}.user_id FROM $wpdb->usermeta 
              WHERE {$wpdb->usermeta}.meta_key = '{$wpdb->prefix}capabilities'
              AND {$wpdb->usermeta}.meta_value NOT LIKE '%administrator%' )", 
            $user_search->query_where
        );
    }
}

add_action( 'pre_user_query', 'isa_pre_user_query' );