How to use casting in GTK+ ?

[Dipak G Patil <dippatil in ibm com>]

Hi All,

I have created a window using,

GtkWidget* gtk_window_new(GtkWindowType
type) ;

Now I want to show the window maximized
so I used, 
void  gtk_window_maximize(GtkWindow *window);

So I used macro GTK_WINDOW(window)where window is
of type GtkWidget *
but it compiles executes but no output.

Could you tell me where I am wrong ?

Also if I have GtkWidget * object how will I use gdk_*
APIs
What is the right way of casting..?

Thanks in advance 
Thanks and regards,
Dipak G Patil.