Thank you, but I need something more complex than enabling/disabling the screen saver.
I want to set the password and set the timeout.

Using SystemParametersInfo I can only set the timeout... I have no idea how to set the screen saver password....

My goal is to control an existing screen saver or to create an application to behave like a screen saver. The later is not easy because for example I don't know how to disable the "Task-bar" key on my keyboard or how to disable Ctrl-Alt-Delete or Ctr-Tab etc...