Hay que tomar en cuenta algo, se recomienda en el mismo anuncio hacer "yum upgrade" ya no "yum update" para actualizar lso paquetes de CentOS 5.0 o 5.1 a los nuevos de CentOS 5.2, sino miren aqui:

http://lists.centos.org

Hay una parte que dice:

+++++++++++++++++++++++
Updating from CentOS-5.0 and 5.1

If you are already running CentOS-5 ( either 5.0 or 5.1 ), all you need 
to do is run :
"yum upgrade" on your machine, and that will bring in the new packages 
from 5.2 and update your machine. Note that the command required is 
'upgrade' and not the usual 'update'. Refer to the yum man page for 
details on how those two differ in operation.

Should the CentOS-Base.repo file on your existing CentOS-5 install be 
modified, you might need to pay more attention to the output from the 
'yum upgrade' command. If the following command produces no output, your 
CentOS-Base.repo file is intact :
rpm -V centos-release | grep CentOS-Base

Lo cual quiere decir:

+++++++++++++++++++++++
Actualizando de CentOS-5.0 y 5.1

Si usted ya tiene CentOS-5 (ya sea 5.0 o 5.1) todo lo que necesita es hacer:
"yum upgrade" en su máquina. Esto llevará sus paquetes a la versión 5.2 y actualizarlos. Tenga en cuenta que el comando requerido es "upgrade" y no el acostumbrado "update".