There is a simple way to install yum, even if you do not have the CD/DVD.
CENTOS 5 64 bits.
Just run
rpm -Uvh http://mirror.centos.org/centos/5/os/x86_64/CentOS/gmp-4.1.4-10.el5.x86_64.rpm rpm -Uvh http://mirror.centos.org/centos/5/os/x86_64/CentOS/readline-5.1-3.el5.x86_64.rpm rpm -Uvh…