How to update RHEL4 with CentOS repository

How to update RHEL4 with CentOS repository.

Q:Why would anyone want to do that?
A:If you have large number of test, qa or development servers you would need to pay millions to get updates for a supposedly free operating system. This is typical nonsense. Big nod here to CentOS people. What they've done is a most sensible thing ever happened to GNU/Linux.

Find nearest CeontOS mirror.

Download and rpm -U two packages: centos-release and up2date from 4/os/xxx_platform/CentOS/RPMS directory.

Edit /etc/sysconfig/rhn/sources and replace all yum repositories with your local mirror, eg.: yum centos4-Base http://mirror.centos.org/centos/4/os/$ARCH/

up2date -u && reboot

Make sure you update your kernel packages as well (not done by default)