From the little help that I can get over the internet, I found out that you need to install the following packages to prepare the system for Webmin installation.
Run the following command over SSH or Ubuntu Desktop’s terminal window (Applications -> Accessories -> Terminal).
sudo apt-get install perl libnet-ssleay-perl openssl libauthen-pam-perl libpam-runtime libio-pty-perl libmd5-perl
(Learn how to configure SSH on Ubuntu 8.10 if you want to have a remote access to your Ubuntu box).
Download the latest version of Webmin by running the following command (visit webmin download section for newer versions)
After the package has been downloaded, run the following command to install it
sudo dpkg -i webmin_1.500_all.deb
You should now be able to login to Webmin at the URL https://localhost:10000/ using root or any other user with sudo access.