If your main window is a dialog, you would want to create it with either the CreateDialog function (for a modeless dialog) or the DialogBox() function (for a modal dialog). You do not want to use CreateWindow.
Is it possible to put a menu object in a Dialogue? I don't see an option for this.
Regardless it seems strange that you can't populate a Window with anything such as buttons or boxes. Perhaps I just have my nomenclature wrong. What kind of a resource would you add to put a button, text box or anything like that in the main window? I was using the Dialog resource in VS2010 because I don't know of any other type.