If you like to install and update Webmin via RPM, create the /etc/yum.repos.d/webmin.repo file containing :

[Webmin]
 name=Webmin Distribution Neutral
 #baseurl=http://download.webmin.com/download/yum
 mirrorlist=http://download.webmin.com/download/yum/mirrorlist
 enabled=1

You should also fetch and install my GPG key with which the packages are signed, with the commands :

wget http://www.webmin.com/jcameron-key.asc
rpm --import jcameron-key.asc

You will now be able to install with the command :

yum install webmin

All dependencies should be resolved automatically.