WordPress 2.6.5 Upgrade: The Easy Way
There is an easier way to upgrade from WordPress 2.6.3 to WordPress 2.6.5. Note that WordPress skipped version 2.6.4 because there was a fake 2.6.4 floating around out there.
From the new WordPress 2.6.5, you can just upload and replace the following files to fix the security issue:
wp-includes/feed.php
wp-includes/version.php