mod_rewrite doesnt work for removing index.php

[eluser]Unknown[/eluser]
I am trying to get rid of the index.php from the url by setting the following:

$config['index_page'] = "";

I am using this htaccess in my root ci folder:

RewriteEngine on
RewriteCond $1 !^(index\.php|images|captcha|css|js|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]

This doesnt work for me. any clues ?