[eluser]Colin Williams[/eluser]
Drupal's form API is far superior to anything currently offered by CI or any contributed libraries. Once you have you head around it, you'll be in love with it.
Your module has a function that defines a form; a function that validates the form; and a function that submits the form. These are the "model". Your hook_menu() implementation is the "controller". And theme_your_form_id() is the "view". Have you tried the Form API quick-start guide?
You could also implement CI's libraries as modules, and possible even the whole (or most of the) CI system, but I don't really see what that affords you. Drupal is plenty capable as a framework, you just have to be comfortable with its aspect-oriented implementation.