WordPress MU

Hello
I need 4 wordpress blogs. To be as the following:
General blog, news blog, photo blog, info blog
Mysite.com\general
Mysite.com\news
Mysite.com\photo
Mysite.com\info

And I want every New User Role to be as a contributor for all bloges by Default.
Can wordpress mu do that?
Any idea please ?

http://wpmudevorg.wordpress.com/project/default-user-role

Edit: you've asked for an idea ;) Well, searching the forum is ALWAYS a good idea :)

VentureMaker
Thank you for help.
Not this what I need. In other words, when someone sinup as a user , must be contributor in all blogs in same time, Not in main blog only.
I need it automatically be a contributor in first , second and third blog.

I guess this's a solution http://mu.wordpress.org/forums/topic.php?id=8948

thank you very much

Automatic registration to multiple blogs as contributor: http://mu.wordpress.org/forums/topic.php?id=9913

thank you dsader

its very useful