Ciao
te falta la mitad, como que el sef te lo gestiona Joomla añadele esto:
[b]RewriteBase /
########## Begin – Joomla! core SEF Section
############# Use this section if using ONLY Joomla! core SEF
## ALL (RewriteCond) lines in this section are only required if you actually
## have directories named ‘content’ or ‘component’ on your server
## If you do not have directories with these names, comment them out.
#
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional – see notes##
RewriteCond %{REQUEST_URI} (/|.htm|.php|.html|/[^.]*)$ [NC]
RewriteRule ^(content/|component/) index.php
#
########## End – Joomla! core SEF Section[/b]
Si en el futuro te descargas un componente sef (sh404, artio, etc…) tendrás que añadir otra parte de unas 12 lineas