RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -d
RewriteCond %{REQUEST_URI} (.*)
RewriteCond %{REQUEST_URI} !^/your/dir.*$
RewriteRule (.+)[^/] %1/ [R=301,L]
RewriteRule \.(css|js|ico|gif|jpg|jpeg|png|swf|mp3|txt)$ - [NC,L]
RewriteRule ^index\.php$ - [L]
RewriteRule .* index.php?go=$0 [QSA,L]