install yum centos 5

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 

How to install NTOP on CentOS 5.5 64bits

Quick and easisest way:
wget http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS//rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
rpm -Uvh rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
yum install ntop
# Get yum ready
yum clean all
yum update
# Install Development Tools
yum groupinstall “Development Tools”
# …

yum to use DVD

Howto use yum  CentOS DVD
To install packages directly from the DVD one must do:
# vi /etc/yum.repos.d/CentOS-Media.repo
enabled=1
# mkdir /media/cdrom
# mount /dev/cdrom /media/cdrom
# yum –disablerepo=* –enablerepo=c5-media …