Today I was installing Virtualmin from the GPL install script (the one you can get from http://software.virtualmin.com/gpl/scripts/install.sh) and the install script exited for the stated reason that my system (a virtual machine) had not enough RAM. This system had less than 1GB RAM.
What the install script also told me was that there is a special --minimal flag you can add to the install script command that will allow you to install Virtualmin on such low RAM systems and it installs a smaller set of packages. That's good to know.
And you can install VIrtualmin in "minimal" mode like this:
chmod +x install.sh
Pretty cool, huh? I'm installing it right now this way and maybe this would also be a good way to install it on other machines that do have plenty of RAM, but where a minimal install is desired.