I managed to activate multisite and to append my htaccess file, but still, in the back-end the Super-Admin menu item is not shown.
php_value memory_limit 256M
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule . index.php [L]
</IfModule>
# END WordPress
Any help appreciated, Thomas