WordPress MU

Do you think is it possible have the same theme for all the blog and change only the style file ?

Yes, I know it's possible.

You don't actually change the style file - you add a new one that hooks into the header and gets run after the original.

here's a post with a TON of plugin choices
http://mu.wordpress.org/forums/topic/13539?replies=10#post-79176

Thanks, and if i want custom text in the theme is it possible have it ?

where?

"in the theme" doesn't really say much.

Custom text where in the theme? It should pull the blogs' name and tagline. Use text widgets for custom text in the sidebar.

And, you know, posts and pages for the rest...

I'm using only a style, but, for example, i'd add a custom line of text in the sidebar of a specific blog, is it possible make this ? And in the loop ? Sorry if i don't speak better and more specific but i don't speak english very well :)

"i'd add a custom line of text in the sidebar of a specific blog, is it possible make this"

Use a text widget in the sidebar.

"And in the loop ?"

Not unless you want to write a plugin that hooks into the_content.