Forms order

I develop medium size form based business application.
I need a solution to correctly manage order of my forms.

In Running Programs there is only one position representing my
application. When user click Activate, system should show top form of
my app and when user close it, system must show previous one and so on.
2. When user run again application, system should do the same thing,
especially when my app has lost focus.

My forms are all preloaded on application start. I only want to
show/hide them when i need.

Any hints?

KW