I'm trying to keep serendipity installed in a subdirectory, but use it as a my home page (keep my root directory clean). I set up htacess like this:

Options +FollowSymLinks
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ /blog/index.php ...