ubuntu-desktop == Ubuntu. Simple enough.
xubuntu-desktop == Xubuntu. Installs Xubuntu
kubuntu-desktop == Kubuntu. This installs, you guessed it, Kubuntu.
So for example lets say you've followed the "cli" install method detailed earlier, and you now want a full ubuntu desktop, simply run:
sudo apt-get install ubuntu-desktop
Lets say you want to install Xubuntu:
sudo apt-get install xubuntu-desktop
This is actually not a bad idea, this gives you a network install with all the latest security patches right out the gate. I always use the mini.iso or netboot.tar.gz, its faster, more efficient, and the most secure way to install Ubuntu.
Its very debatable as to what is the most lean desktop environment. In my tests, and I've had other people and other articles confirm it, Xubuntu only uses slightly less resources than Gnome with desktop effects turned off. On a lot of machines, ones with 256 megs or lower, this could pose a problem.
However, for me, I wanted to run xfce 4.6, the latest XFCE release. Even though Xubuntu uses XFCE, they are actually seperate projects. To install XFCE without all the extra Xubuntu stuff, simply run:
sudo apt-get install xfce4
This will be a VERY bare minimal desktop environment. Its basically the same set of xfce4 packages that Debian uses. This install doesn't even have a consistent icon set. I recommend tango:
sudo apt-get install tango-icon-theme
Once its installed, you can set the icon theme in Settings - Appearance and go to the Icons tab. Click on "Tango"
There you have it. Now you need to install a web browser, and other applications your accustomed to. I recommend doing this one application at a time. It keeps your system very lean. Use "apt-cache search" to find your applications.
Now, onto network manager. I've resisted installing this application because I felt I was beyond it. I was actually wrong. And don't worry about resources, NetworkManager only has a rss of a few megs, I'm sure you can spare the change.
My main reason for installing it was my laptop. My networks sometimes, and sometimes don't, reconnect after I unsuspend my laptop. There seems no rhymne or reason to it, it just simply won't reconnect.
To install, I simply ran:
apt-get install network-manager network-manager-gnome
and presto, it was running in my system tray next time I started my X session.
Just one caveat: Make sure you comment out any configuration you may have done earlier in /etc/network/interfaces. The auto lines are all you need.