Is kbuntu part of the regular ubunto package? If it is, how do you incoke it?

An older version of Kubuntu was easier for me to use.

I downloaded the iso from kubuntu.org

You can just install the meta package from synaptic and run the two
different desktops if you want to flip from ubuntu to kubuntu. But
i've had one or two probs in the past from running two desktop
environments.

I think so (at least for what could be called "KDE kernel")
because Ubuntu let people choose between Gnome
(default provided desktop manager) and KDE.
And Ubuntu + KDE = Kubuntu. Though it is posssible to have both
completely installed (but such configurattion is a bit difficult
to deal with).
As for me I use Gnome, because I'd rather
have a nice graphical interface, but some of my programs use
KDE because there is no different way to run them.
Ubuntu has a minimum of default configuration for KDE
and there is nothing to setup for running KDE programs
with Gnome.
The inconvenient is that their graphical interface is
really poor, but you can slightly improve it by choosing
some convenient colour in gnome setup.

On the login screen, click bottom left hand corner and select 'sessions'
then select 'change session' and select 'Kde' which is 'Kubuntu'