Rob Allen has posted a look at working with modules in the Zend Framework. His specific goal is to work with a model that's inside a module from inside another, different module (clear as mud? keep going!)
I've started to play with modules in a Zend Framework 1.8 application as the new autoloader means that all your model directories no long have to be on the include_path for autoloading to work. What I'm specifically interested in is being able to instantiate a model that is within a module from within another module. Setting it all up isn't that hard, but I couldn't find a concise description, so these are my notes on it.
To get it all working, he sets up things from the beginning - creating a new project, making a new model inside the module and linking it to the controller with the magic of autoloading. This last part does require a bit of work - you'll need to update your configuration files to let the framework know about this directory and make a bootstrap instance (extending Zend_Application_Module_Bootstrap) to pass the requests through.