$count_user=Doctrine::getTable('sfGuardUser')->count();

$first_day_of_current_year = date('Y-m-d H:i:s', strtotime('1 january'));

$q = Doctrine_Query::create()
  ->select('COUNT(u.*)')
  ->from('sfGuardUser u')
  ->where('u.created_at > ?', $first_day_of_current_year);
$total = $q->execute(array(), Doctrine_Core::HYDRATE_NONE);
$total = $total[0][0];