WordPress MU

Hi all, i've found some discussions about this, but i haven't found a solution.

The problem is simple: i want that ALL my blogs will have locked post-categories: movies, theatres, arts.

When an user makes a new post in his blog, he should only choose between these categories, that are ready to be used in each blog.

I need this because in my homepage i show posts from all blogs, divided by category, and so i need they are all categorized in the same way.

It would be cool to have the same thing for "general tags" (bloggers could only choose between predefinited tags for their posts), but for now categories could be enough.
Thanx all!

Youd need to code a plugin that creates those categories for every new blog and also hide the categories page so they can't create or delete categories. Definitely possible and not too difficult, but I don't have time to provide you code. Here's an example of how to remove menu items:

add_action( 'admin_menu', 'remove_permalinks_menu_item' );

function remove_permalinks_menu_item()
{
    global $submenu;
    $submenu['options-general.php'][35] = '';
}

And adding categories will require adding data to wp_x_terms, term_relationships, and term_taxonomy, as they all work together.

Really thanx Brian. I'm not able to modify wordpressmu cause i'm ignorant in php or js, but if someone will write in an easy way these pages i will be eternally grateful, and i think that a lot of thematic wordpressmu admins would like to create organized blogs for their users.

I've alreay created an external blog that creates the sitewide feed, using the sitewidefeed plugin.

Could i use that external blog as reference for categories too?
Example: i set categories on that blog, and they are extended all over the blog network?

Or could i make categories "static", hardcoding them in wpmu php (but i don't know how)?

How about this:

http://wordpress.org/extend/plugins/user-cats-manager/

thanx musnake.
I'm afraid that plugin can be useful only on Wordpress and not on MU. I don't think it can create a bunch of default categories when creating a new sub blog...that is the main goal of my topic.