hey,

either I have misunderstood the idea of Zend_View or render, or something is working wrong here.

Let's assume:
http://localhost/module/main

shoould invoke method mainAction() in ModuleController.php, right? right.
then inside it i'm writing:

function mainAction() {
$view = new Zend_View();
echo $view->render("s.phtml");
}

My expected result is then to get s.phtml rendered only.
Instead, in the output I can see main.phtml + s.phtml.
Why?

You have to turn off the viewRenderer, put this in your bootstrap file.