The screen application can be used to make sure users do not leave accounts logged in. You can set an automatic log out when an idle time has been reached.
This example of a minimal desktop shows how to manually create partitions using ext3 and ext4 for a server that has a minimal desktop for a graphical interface.
There are a lot of new options to explore in CentOS 6 during install, be sure that you have a basic understand of what the options are before you begin the installation.