Hi Diemmess, your usual respondent here! :-)
Do you mean that you want flyout submenus to expand out of the existing navigation bar, or would you prefer the new pages to be added to the existing navbar?
Don't worry to much about the effects of site structure if you want the latter, though it is very important if you want the former.
Your new pages can be added to each individual navigation bar by experimenting with the different settings on its properties palette: for example, you can change the page level that it uses, you can remove the index page from the menu, or go for the custom option. I usually go for that, as it guarantees getting the pages that I want.
When setting out your custom links, you can play around with their placement and even attach them to other pages (by a click and drag approach) if flyouts are used.
click here for an example of flyouts on one of my sites. Used here to categorise pages under section headings, if you will, and avoid huge navigation bars running down the side.
As always, feel free to ask me for more info if required.