1.) Log into your server. You can use SSH or your TTY.
2.) wget http://prdownloads.sourceforge.net/webadmin/webmin_1.340_all.deb
3.) sudo dpkg -i webmin_1.340_all.deb
4.) If you get errors, just type sudo apt-get install -f (this will install all the required pre-reqs)

EDIT: I had this as 8.06 server, when in fact it’s 8.04. My mistake. And since I always seem to install this right after installing the server, it’s a good idea to apt-get update, then apt-get upgrade

EDIT PT 2: The newest package is webmin_1.430_all.deb

EDIT PT3: if you’re installing on a CENTOS 5 box (like I am right now), you’ll need to wget http://downloads.sourceforge.net/webadmin/webmin-1.430-1.noarch.rpm
and then rpm -i webmin-1.430-1.noarch.rpm

EDIT PT4: Newest package is webmin_1.470_all.deb (http://prdownloads.sourceforge.net/webadmin/webmin_1.470_all.deb)

EDIT PT 5: Newest is webmin_1.490_all.deb (http://prdownloads.sourceforge.net/webadmin/webmin_1.490_all.deb)