unless you buy the required license ( $49 to $299)
you do not install anything that is not on the "out of date" dvd - NO current security updates
RHEL 6.3 is the current ( 2012-06-20)
if you have a rhel6.0 it came out on "2010-11-10"
and is two years ( almost) out dated
if you ARE taking the RHCE
BUY the red hat license and you also might want to buy the red hat books and testing tools for the test
thought you could "get away" with installing CentOS 6.3 .
You will get NO experience using red hat's RHN
Nor any experience in registering a red hat install
also if you buy the required license you also get access to the redhat knowledge base
( some is open to the public- but only a small part)
or port the CentOS wiki for use on RHEL