It is actually very easy to install webmin on the new Ubuntu 10.04 LTS Server. Here is what you will need to type
Login to your server and update your server
apt-get update
apt-get upgrade
apt-get dist-upgrade
Then you can get the and install webmin
wget http://downloads.sourceforge.net/project/webadmin/webmin/1.510/webmin_1.510-2_all.deb
sudo dpkg -i webmin_1.510-2_all.deb
Then if there are errors then type the following commands
sudo apt-get install -f
Then you are good to go. Make sure you have noted your IP address so that you can login from your browser at
http://yourip:10000/
Enjoy