Controller A loading a view which has data from controller B

[eluser]tobefound[/eluser]
Pretty self-explanatory:

Controller A is loading a view which presents data from controller B? How can this view get its data from controller B when I'm calling the view from A?

The problem comes from my site displaying multiple forms at the same page. For instance, I might have a login form visible at the same time as the registration page is visible (having the login form in a side panel).

Anyone can shed some light?

/Tommy