Getting Webmin is easy, and in fact, it may already be installed on your system. Several Linux distributions now include Webmin as either its primary system administration interface or as an optional package. Also, a large number of Linux hardware vendors use Webmin or a modified version of Webmin as their network interface. However, because Webmin is Free Software, even if you don't already have Webmin, it is only a download away.
It's often best to obtain Webmin from your OS vendor, if they provide a package for it. In this way, you can be sure it is automatically configured suitably for your particular OS and version. File locations vary somewhat from version to version and from vendor to vendor, so getting it from your vendor insures a consistent filesystem layout.
If your OS or system vendor does not provide a package of Webmin, then you can go to the Webmin homepage at: http://www.webmin.com/webmin. Here you will find the latest version of Webmin in a tarball package, a Solaris pkg, as well as an RPM package. The tarball will work on nearly any Unix version that has Perl, while the RPM package is known to work directly on at least Red Hat, Mandrake, and Caldera versions of Linux.