Mambo only has a two-tier hierarchy of Sections ->Categories at this stage. BUT, there are ways you can manipulate things so you have the appearance of what you want. To do this, you need to look at how you want your content linked to from the menu.

For example, you may decide to have a static page linked to on the menu, that might include links to your sections.

Or, say you want something like this:

Stories
Genre
Author

If Stories is really only a menu link, then you can have your Genre as Sections and your Authors as Categories.

Or you can do something like this:
Section
-->Category
--->Content Item containing just links to another Section
----> Section that is not in menu, but only linked to from above
-----> Category
------> Content Item

So, you see that although there is a limitation of only the two tiers, these can be worked around quite nicely.

One very large Mambo site manages its Sections and Categories this way:
Section
--> Categories
--> Content Items
----> Categories
----> Content Items
------> Categories
------> Content Items
--------> Categories
--------> Content Items
----------> Categories
----------> Content Items

This example uses one section containing 800 categories, nested by parents in the navigation menu.


Note: there are other ways of handling this too, its just a matter of playing with your menu so you can get the structure you prefer. If you think about the categorization from the user experience and remember that navigation is all menu-driven, you will find that there are many ways you can present your content as if it is in multiple categories.