Quite simple : You will not be able to use Fedora 12
packages on CentOS 5.x. They depend on glibc-2.11.
CentOS 5.x has glibc-2.5. (Which cannot be changed.)
So you have just been lucky, that the packages also
require a quite different "rpm command".
Cannot be installed with the old CentOS 'rpm'.
The latest update, CentOS 5.5: gcc44-4.4.0-6.
http://mirror.centos.org/centos/5.5/