Gnome and KDE

I learn about different X window environment. Still I start with Ubuntu with Gnome, I gather from https://help.ubuntu.com/9.04/config-desktop/C/other-desktops.html that I can Using KDE or Xfce instead of the GNOME desktop So I download and test out. One mistake is that I answer "using KDE" as default window manager of that sort. KDE does not run well on my ATI video But it give a similar interface as puppy Then I struggle to change back to Gnome default AT last I found http://ubuntuforums.org/archive/index.php/t-1155162.html I think Gnome is ok Microsoft has the advantage at this moment as the task bar can be below as in KDE or pull up to the top as Gnome. But I believe X window will one day be able to do so. But at this time of writing the blog, I am not able to remove the KDE even though I shutdown to single user mode and run # apt-get remove kde-core I still reboot into KDE environment At the login screen, I have to struggle to login and change the screen to Gnome Quite miserable ... But I have to bear with it for the time being. Then I finally found the right term - default login manager and found this http://ubuntuforums.org/showthread.php?t=613148

sudo dpkg-reconfigure gdm

sudo /etc/init.d/gdm start