Configure config.php file:
$config['sess_driver'] = 'redis';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_save_path'] = 'tcp://localhost:6379';download the extension:
http://windows.php.net/downloads/pecl/releases/redis/3.1.1rc2/
configure php.ini
to test, its good to use the php server standalone: php -S localhost:9090
using apache, doesn't show messages about errors when loading the extension.