Matthew Weier O'Phinney and Lee Brimelow will be giving a free webinar tomorrow (Wednesday, Oct 22nd) covering the Zend_Amf component of the Zend Framework.
They'll go over the Zend Framework and the Zend AMF module that allows PHP developers to connect Flex applications to Zend Framework powered applications using AMF. You have to register for the e-seminar to attend.
You can find out more about using Flex and the Zend Framework together in this section of the Adobe website.