WordPress MU

hi,
I have a subdirectory named shop in my public_html folder.
Wordpress MU for certain pages redirects me away from the shop folder and back to wordpress MU.
How can I tell wordpress MU to ignore the shop folder with htaccess?

I assume VHOST = true...
I assume no fancy conf file redirwitchery

# Lock WPMu out of the following subdomain directories...
# This must occur before the final rewrite of
# http://www.domain.tld to domain.tld
#
# You must also specify 'shop' as a forbidden blog name
# in mu admin

RewriteCond %{HTTP_HOST} shop.domain.tld
RewriteCond %{REQUEST_URI} !shop/
RewriteRule ^(.*)$ shop/$1 [L]

# I'm pretty sure this is in the readme...