These are supplement notes I had taken down a while back doing an install of nagios and n2rrd on a Fedora-7 box and recently came very handy when doing the install in a redhat (RHEL-3) box as well:
Nagios Install:
# yum install nagios nagios-plugins nagios-plugins-http nagios-plugins-icmp nagios-plugins-ping
On RHEL3, I used (dags rpms) rpmforge. Here is my yum.conf for rpmforge:
[rpmforge]
name = Red Hat Enterprise $releasever - RPMforge.net - dag
baseurl = http://apt.sw.be/redhat/el3/en/$basearch/dag
Notes: I settled for icmp instead of ping, as it is a lot faster. However, icmp required setting setuid for "/usr/lib/nagios/plugins/check_icmp" for it to work. Also, had to rebuild nagios-plugins from source as root in order for the plugin to be installed.