By "i do not have yum" I'm assuming you mean that you do not have munin / munin-node available in an installed yum repository. That is true by default. I would suggest installing the EPEL repository.
I have directions for installing it here (you'll just need to change your URLs for RHEL4 as below):
http://ridingthecloud.com/installing-epel-repository-centos-rhel/
Install RHEL4 EPEL on 32-bit Systems:
sudo rpm -Uvh http://download.fedora.redhat.com/pub/epel/4/i386/epel-release-4-9.noarch.rpm
Install RHEL4 EPEL on 64-bit Systems:
sudo rpm -Uvh http://download.fedora.redhat.com/pub/epel/4/x86_64/epel-release-4-9.noarch.rpm
Once you have installed the new repository you should be able to install Munin via yum pretty easily. The command should just be:
yum install munin munin-node
More details here:
http://ridingthecloud.com/linux-server-performance-monitoring-munin/