Hi Mika,
I have two .htaccess's due to my host's file structure (one to direct everybody to the right folder, and the WordPress one).
Here's the top-level one:
RewriteEngine on
order allow,deny
allow from all
#php_flag display_errors off
Options -Indexes
Options +FollowSymlinks
RewriteEngine on
redirectMatch 301 ^wordpress/eng/category/conny-van-ehlsing-monster-hunter/feed/$ http://www.dreadfulgate.de/wordpress/eng/feed?cat=577
RewriteCond %{HTTP_HOST} !^www\.dreadfulgate\.de$ [NC]
RewriteRule (.*)$ http://www.dreadfulgate.de/$1 [R=301,L]
(I've cut a few more feed redirects because I've checked for those and to make it more readable. They're pretty much like the one I kept.)
Here' the WordPress one:
RewriteEngine On
RewriteBase /wordpress/
RewriteRule ^index\.php$ - [L]
# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]
Those files were the first place I looked for clues, of course, but maybe (hoepfully!) you can see something I didn't.