Accessing the stage?

In my FLA I have a document class called Main.as. I created a class called MainNav.as and imported it into the Main.as class. I am having trouble trying to access stage.stageWidth value from the MainNav.as class. Anytime I try to get the value I get an error.

The only way I got it to work was, if I created an empty MC in my library then attached the MainNav class to the MC. When I do it that way I can no longer import it into the Main.as class, unless I want it to error out.

What I am trying to do is convert my AS 2 site to AS 3. I have it set up in AS 2 so that the site loads the xml then dispatches an event to animate the nav. In AS 3 I am not sure if I can do it that way if I link the MC to the class and not import into my Main class.

Thanks