The CentOS DVD images (not sure about CD images) have an images directory that contains a boot.iso file that can be used to net boot machines. That's the one I used.
Together with a combination of autofs, lighttpd, rsync'ing and cron I am able to fully support a lab of about 500 machines and a small cluster using just 10 boot CDs and some kickstart files, boot and update the machines in about an hour. Including system customization, also done through shell scripts.
have you had a look at cobbler and koan? They will do all this for you automagically