Permalinks and URL re-writing

Hi everybody,
I’m new in WP community and i’m trying to set up my first blog.

I just have a problem with permalinks. Indeed, i get a 404 error each time i want to activate personals permalinks.I’ve tried to save another time the settings, but nothing to do, it does not work.

URL rewriting is activated, and here is my .htaccess in /var/www/wordpress, the directory where wp is :

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /wordpress/
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /wordpress/index.php [L]
</IfModule>

# END WordPress