I've some X quantity of blogs setup within the Wordpress MU . I have to install styles for each one of the blogs.

How do you install styles on their behalf? Basically install within the primary directory does it work for the blogs or I have to install for each one of the blogs individually once we do within the traditional Wordpress.

Please tell me for plug ins too.

Put them within the wp-content/themes directory. After this you have to enable them within the admin user interface, via Site Admin > Styles. This enables any blog within the system for their services.

Plug ins put into wp-content/mu-plugins are instantly enabled for those blogs within the system. They can't be switched off through the customers.

Plug ins put into wp-content/plugins could be enabled on the per-blog basis if allowing the consumer to do this in Site Admin > Options > Menus.