Multi-page form with Yii in a Craft site?
I wouldn't worry going so far outside of Craft and using Yii's forms.

Sounds like all you need is a Craft plugin.  Use normal HTML &lt;form&gt;s from  your template and have them post to your plugin's Controller.  Each step in the form can be another action on the controller.  You can persist data between form steps by saving to Craft's HttpSessionService, which is just a thin wrapper for PHP's global $_SESSION variable.

craft()-&gt;httpSession-&gt;add($key, $value)


and:

craft()-&gt;httpSession-&gt;get($key)