смотрите http://blog.tyshkan.ru/2009/05/%D1%81%D0%BA%D0%BE%D0%BB%D1%8C%D0%BA%D0%BE-%D1%81%D0%B0%D1%85%D0%B0%D1%80%D0%BD%D1%8B%D1%85-%D0%BA%D1%83%D0%B1%D0%B8%D0%BA%D0%BE%D0%B2-%D0%B2-%D0%BA%D0%BE%D0%BA%D0%B0-%D0%BA%D0%BE%D0%BB%D0%B5/