Zend Optimizer

Ok, I've searched the archives and even contacted the Zend staff on this one, and I'm still confused. I also posted this question at the Zend Optimizer Forum but have not received an answer. I'm hoping one of you has some idea of how the Zend Optimizer works and can explain it. My webhost offers PHP 4 on Linux/Apache with the Zend Optimizer (v0.99) Engine (v1.0.3) and I have checked phpinfo() to make sure it's installed and running. I would like to optimize a particular function that generates a graph image on the fly. What do I need to do make use of the Zend Optimizer? Is it used automatically or do I first need to compile the code into a binary file? If someone knows a great source of info on this (other than www.zend.com), that would be helpful too. Thanks, Johan Alfredeen