Form autocomplete

Hello everybody.
I have interesting problem. I need to create form with auto complete text field.
I have the data table in database with next fields | nid | login|
And when i type login nothing happens.
here my code:
function my_search(){
global $user;
$form['name'] =array(
'#type' => 'textfield',
'#title'=>'User login',
'#size'=> 9,
'#autocomplete_path' => 'my/autocomplete/',
);
$form['submit'] = array( '#type' => 'submit', '#value' => t('Search') );
return $form;
}
function my_menu(....){
$items[] = array('path' => 'my/autocomplete',
'title' => t('Autocomplete '),
'callback' => 'my_autocomplete',
'access' => user_access('access content'),
'type' => MENU_CALLBACK);
return $items;
}
function my_autocomplete($string = '') {
global $user;
$uid = $user->uid;
$regexp = '%(?:^|,\ *)("(?>[^"]*)(?>""[^"]* )*"|(?: [^",]*))%x';
preg_match_all($regexp, $string, $matches);
$array = $matches[1];

// Fetch last tag
$last_string = trim(array_pop($array));
if ($last_string != '') {
$result = db_query_range("SELECT t.login, t.nid FROM {my_table} t WHERE t.uid = %d AND LOWER(t.login) LIKE LOWER('%%%s%%')", $uid, $last_string, 0, 10);
$prefix = count($array) ? implode(', ', $array) .', ' : '';
$matches = array();
while ($tag = db_fetch_object($result)) {
$n = $tag->login;
// Commas and quotes in terms are special cases, so encode 'em.
if (strpos($tag->login, ',') !== FALSE || strpos($tag->login, '"') !== FALSE) {
$n = '"'. str_replace('"', '""', $tag->login) .'"';
}
$matches[$prefix . $n] = check_plain($tag->login);
}
print drupal_to_js($matches);
exit();
}
}
How i can do it?
And what wrong with the code?