Loading controllers from within controller

[eluser]sanguina[/eluser]
How do i load a controller from within a controller.

For example,

I am using tank_auth library which has a controller called auth which calls a view called login_form to display the login form page.

Now I want to display this login form in the top of the homepage.

the home page is displayed by another controller called home_controller

how do i call the auth controller from the home-controller.

Please help