Jani Hartikainen has posted a guide to his blog for getting the FCKeditor integrated into your Zend_Form instance.

How to use FCKeditor, or any other WYSIWYG editor, with Zend_Form? Another relatively common question. There are many ways you can do this, but let's look at these two as they are the best in my opinion: Adding some JavaScript to your view script, Creating a Zend_Form_Decorator. We'll be using FCKeditor, but you can apply the techniques shown to others, such as TinyMCE, as well.

The first method, via javascript, just drops the editor in inside some script tags. The second (more "Zend Framework way") creates a decorator as a custom way to insert the same javascript code. A call to appendScript inside the render() function (the code is here). Then its just a call to addDecorator to plug in a CU_Form_Decorator_FckEditor instance.