To disallow a directory listing although, just place a blank index.html file in the directory.
To disallow one file (type) then you need to use htaccess
IndexIgnore *.gif *.jpg
Will stop showing any gifs or jpgs in the directory listing.
I guess this could be used for your problem
but haven’t tried it.
EDIT: A note that this will stop header.html appearing in all of your child folders as well. If this is a problem, then you can put the following htaccess file in the folders where you want header.html to appear