There seems to be quite a confusion on how to set clean urls in Drupal 7. You don't need to edit the .htaccess file to get this. Drupal is made to take care of it. Try the below solution and you should be good to go.
This is quite easy:
Just go to http://www.your-site.com/admin/config/search/clean-urls, instead of http://www.your-site.com/?q=admin/config/search/clean-urls and turn it on. No need to change Apache settings.