WordPress MU

excuse me if someone have already post this question or if it is soooo simple but i'm new and i can't working out.

so, very simple:
i want that a new user belogs to all the blogs of my wordpress installation (6 blogs), automatically, when he register, not only on he main blog.
i try with plugin blog register but i think it doesn't work (or i don't understand how)

someone can help me?

Try: http://mu.wordpress.org/forums/topic/13675?replies=17

i found also this, that works.
http://mu.wordpress.org/forums/topic/9913?replies=27#post-85161

thank you very much tim!