[CentOS] Cloned Centos Boxes - First Run to run again?

Sun Jan 10 11:26:29 UTC 2010
Mr Gabriel <gabriel at impactteachers.com>

I need to build a bank of 12 centos boxes, for an experiment I'm doing. 
I don't want to install centos 12 times, I'm using virtual box across 
three machines, how can I get the first run scripts to run again to that 
the box is reconfigured on it's next boot.

I want each box to appear like a fresh unique install.