Webmin does not include Virtualmin. Virtualmin runs on top of Webmin, and must be installed separately--though if you use the documented method of installing Virtualmin, you don't need to install Webmin, as it will be automatically installed during the Virtualmin installation process.
And as noted, you would access Virtualmin on the same port as Webmin; Virtualmin installs a new theme that provides a link in the upper right corner to switch between Virtualmin and Webmin views. Usermin is a webmail client (plus some bonus features), and it runs on port 20000.
We strongly recommend you install Virtualmin using the automated install script we provide on the Virtualmin website, rather than trying to configure it manually...unless you have a extremely high level of Linux and virtual hosting experience and knowledge, configuring it manually is an error-prone and very time-consuming process (even if you do have that experience and knowledge, it's still going to take hours to complete the configuration if you do it manually):
http://www.virtualmin.com/download
With the install script, it takes 5-20 minutes, depending on the speed of your network connection. But, it does require a freshly installed supported operating system (
http://www.virtualmin.com/os-support), since any preconfigurationn of Apache, Postfix, etc. will probably cause unpredictable behavior and possibly brokenness after the installation completes.