sudo apt-get install libnet-ssleay-perl openssl libauthen-pam-perl libio-pty-perl libmd5-perl
wget http://prdownloads.sourceforge.net/webadmin/webmin_1.350_all.debIf this does not work, there is probably a newer version of Webmin. Get the link to the latest *.deb file from the Webmin site.
sudo dpkg -i webmin_1.350_all.deb
You will get the following output:
Webmin install complete. You can now login to https://your-server-name:10000/ as root with your root password, or as any user who can use sudo to run commands as root.