Subdirectories and domain mapping

Hey all!

I’ve got a little problem establishing my new WPMU. I hope someone will be able to help me!

Context: Apache Server running WP3.0.4 with Multisite enabled (using subdirectories).
WP is in: /var/www/blogs/, accessible by blogs.domain.fr (I’m french!^^)

With the same domain, i get the original vhost to: /user/domain/www/…

I have few blogs. and one is: blogs.domain.fr/domain-fr/, the original blog of the domain.

I would like to have the blog accessible from: domain.fr/blog/

1/ First Solution: HTACCESS!
I tried the following htaccess at: /user/domain/www/blog/.htaccess

RewriteEngine On
RewriteBase /
RewriteRule ^(.*) http://blogs.domain.fr/domain-fr/$1 [P]

In the configuration of the blog domain-fr, i have: domain=blogs.domain.fr, path=/domain-fr/, siteurl=http://domain.fr/blog/

That solution is working if I disable permalinks, if not, i get the correct page but articles or pages are 404 Not found!

2/Solution 2: Domain Mapping
I tried to use this tutorial:
http://wordpress.org/support/topic/how-to-map-a-domain-with-subdirectory-to-a-multi-site-network
Which seems really near my own query! But i get confused in the modifications made, and my real need.

Does someone has a solution? I hope!

Have a good day,
Corentone