Installing KDE desktop on Ubuntu
One of the best feature of Linux is separation of Kernel layer and Presentation Layer(Desktop). You can use desktop of your choice without disturbing existing applications. KDE and GNOME are two desktops which are common in almost every distro of Linux. KDE is older and heavy weight while GNOME is new and light weight. You can read further about these two and other desktops in this Wiki article.
Frankly speaking,when I used both KDE and GNome in Redhat 5.5/6.0, I was not impressed much from GNOME and it was because I came from Windows environment. I also didn't like Glade environment for GTK based programming. I found QT, wrote programs in it and enjoyed a lot because it was like Visualbasic for Linux with neat and clear Object Oriented GUI toolkit for C++,since then I always preferred KDE over Gnome.
When I installed Ubuntu first time, I didn't know that it doesn't have KDE insalled. Unlike Redhat which provides both desktop+enlightenment desktop in same CD(s), Ubuntu was based on Gnome desktop environment. I tried to find out some option to switch over KDE but found no option. After searching on net, I found that KDE version has been shipped separately and it's call kUbuntu where K indicates the KDE version of the distro. So, what could be done? I really didn't want to use Gnome and wanted to see my old kde based desktop. Again, I gooled and found out that there is a way to install KDE based dekstop on my existing Ubuntu system. All I needed to install KBuntu Desktop.
For that, I installed the desktop by running following command.
sudo apt-get install kubuntu-desktop
That's it! It installed necessary dependencies and after reboot, I had my KDE desktop available :-)