Delete Main Blog and rewrite it's URL

Hi, I'd like to remove (or by-pass) the main blog and redirect it's URL to a subdirectory

something like:

http://*.mysite.com -> WPMU

I added these lines at the end of .htaccess:

RewriteCond %{HTTP_HOST} ^mysite.com$ [NC]
RewriteRule (.*) dir/$1 [L]

But it seems to work only for files in "dir" and not for subdirectories

Thanks

PS sorry for my bad english

WordPress MU