This article explains how to install New Relic on a Redhat or CentOS 64bit server.
rpm -Uvh https://yum.newrelic.com/pub/newrelic/el5/x86_64/newrelic-repo-5-3.noarch.rpm
And then:
yum install newrelic-sysmond
Edit the configuration file to add your key. Edit the “/etc/newrelic/nrsysmond.cfg” file.
license_key=REPLACE_WITH_REAL_KEY
Enable and restart New Relic:
chkconfig newrelic-sysmond on service newrelic-sysmond restart