Options -Indexes
DirectoryIndex index.php

RewriteEngine on
RewriteCond $1 !^(index\.php|css|js|flash|assets|captcha|resources|apc|images|img|robots\.txt)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L,QSA]