Ubuntu is available free from Canonical. You can download the ISO if
you have a fast connection and burn it to CD the same day or you can
have them mail you one which can take you 10 weeks. They will even pay
the postal costs!

The difference between Ubuntu and Kubuntu is one of preference, Unlike
Windows, Linux offers the user choice. In this case, you are choosing
between two different desktop managers. Ubuntu uses Gnome and Kubuntu
uses KDE.

KDE and Gnome offer different desktop experiences and I suggest that
you try them both out. Ubuntu and Kubuntu install from Live CDs. That
means the computer will boot to a fully functioning version of the
operating system that runs from the CD. You can then see what works
best before you bother to install it to the hard drive.

Gnome is thought to be simpler while KDE is thought to be more robust,
but these are broad oversimplifications. Most people prefer one or the
other, but they like features of each.