The top box is for your user name, and the other is for the password.

thanks, I'll try that if/when I get to the same place after reinstlling ubuntu
(done) and KDE (third time today).

How silly of me not to know a pencil and paper means "type your username. Only
an imbecile could understand that!

Reinstalled, kept old login manager which does NOT mean keeping the old desktop.

If you don't care for Ubuntu 12.04 desktop, perhaps you should consider the
Kubuntu 12.04 Live DVD and install from it, if you like it? It should offer to
add to Grub beside your Ubuntu, etc. or allow you to replace Ubuntu on your hard
drive.

Or if you add Synaptic from the Ubuntu Software Center, if it's still called
that. Then in Synaptic you can add Metapackages, which are Kubuntu, Lubuntu, and
others. Then when you boot your computer there should be a way to select which
one you want to try.

I did this later with the Bodhi Linux, which is built for older computers, I
added Lubuntu as backup to its Enlightenment desktop and lots of my favorite
games, mouse cursors, screensavers, and backgrounds. I added so many KDE
applications that it also offers that desktop to me.

I am not sure why you are re-installing so often. I suspect that this is
unnecessary. The practice may be good though.

The basic underlying structure of Ubuntu and Kubuntu are the same. They
have the same kernel and boot processes. You will see a different graphic
when it boots, but that is just for show. The login screen may be different
depending on the decisions made when installing, LightDM or KDM. It only
changes substantially when you login. This is because Kubuntu uses a
different window manager and different desktop environment to what Ubuntu
uses. Each DE has a distinct look and feel and has its own applications to
support it. For example KDE and Unity have different file managers (KDE =
Dolphin, Unity = Nautilus) and burners (KDE = K3B, Unity = Brasero). The
same can be said for browsers and office and media applications. You
can install and run the applications from the other DE if you prefer.

To install a different desktop environment you do NOT need to re-install.
You can even install Linux Mint (a different distribution) by adding its
sources to your software sources. I do not advise that until you understand
things a bit better, though. I am just pointing out how flexible the
process is.

Kubuntu: uses Kwin as its window manager with its own built in compositing.
It supports plasma workspaces. The desktop environment is KDE.
Ubuntu: uses Compiz as its window manager which also supports 3D
compositing. It does not have plasma workspaces. Its DE is Unity.

By comparison Windows has only one window manager and desktop environment
and replacing it is not easy. Windows Explorer is a combined WM and DE and
supports compositing -- since Vista. There are third party replacements
such as Window Blinds, but MS does not want you switching and makes it as
difficult as they can to ensure that users stick with their gUI.

Other Linux desktop environments to play around are:

GNOME: Uses Mutter as its window manager and GNOME shell as its DE.
Xubuntu: Ubuntu with XFCE as the DE.
Lubuntu: Ubuntu with LXDE as its DE.

Once you understand the principles in installing a new graphical front end
and how to switch from one to the other the fun never stops.
There are many more desktop environments than this and all can be added.
Not all are user friendly. Be forewarned.

The advantage of having more than one DE installed is that if one breaks it
can be fixed by logging into the other one and you do not have to resort to
the commandline to fix it. Breakage is rare, though. Often a reboot will
fix most problems.

Linux is the most fun that you can have for free!

L> I got a little dialog with two text boxes. Only labels: by the top
L> box an icon of a pencil writing on paper. By the lower box a
L> padlock (closed).

the top on is for your username and bottom one for
password but you should also have another icon in the box that gives a
drop-down list when clicked so you can select the desktop you want to
boot into. Select KDE then enter username / password and press Enter.

Next time you boot and want to go into KDE again just give username
and password.

BTW - this entering of Username/Password is well ingrained in the Unix
world which Ubuntu is a child of. If you have only a single desktop
then you can elect to log in automatically but when there's more than
one choice you have this selection / login screen.