So here are some dead easy ways of getting munin and munin-node installed on your RHEL5 server.
First add RPM Forge repository
rpm -Uhv http://apt.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.i386.rpm
Then just fire
yum install munin munin-node
Now, you have your munin running. Lets turn our attention to monit.
First add this new repo to you
rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm
Then go ahead and install monit using
yum install monit
Now this my friend was real easy ! Have fun , more later.