This is what I found for " sub categories in Joomla"
Could jReviews work with it?
Found it over here....http://forum.joomla.org/index.php/topic,10894.0.html
For big sites, there is always the possibility to organize your content differently, by thinking differently (not starting from the technical Joomla limitations/setup, but from your content..).
Define which content groups you need (items 1,2,3,.. in each of site a,b,c,..., all in national park x, which is in national parks east (others being for ex. west, south, norht, center.. etc etc).
Then, start setting up your sections/categories on an as-low-as-needed sublevel, for ex. section = national park x, categoeries = site a, b, c, .. and the individual items.
Now, you'll see you're missing the super-levels of national parks east, and if requiered, national parks (2 more levels). These you can fake by creating the corresponding section and category, with a description for each, and you will set up the hierarchy you want (to show to the user) by selecting the requiered "parent" when you make the menus.
Ex: menu link 1 = parent of all other: National Parks (section with one cat').
This will be parent of the National Parks East (cat' in previous, empty)
This in turn will be parent of (this is where your real content starts!) National Park x (section)
Which is parent of Site A (category)
which finaaly holds your content items..