Since Gnome upgraded to 2.28 in Ubuntu Karmic,the old GDM setup utility missed most of functionality,although there are some articles show how to manually change login interface in Ubuntu Kamic.GDM2 Setup is a login interface management utility for the new GDM, allows for wallpaper setting, autologin option, prompted or userlist login, etc.
The setup utility that comes in Ubuntu Karmic (and many other Gnome based distros) is missing most of the older GDM setup utility’s functionality. This application puts the functionality back in the hands of the users through a familiar and simple GUI.
To install GDM2 Setup in Ubuntu,open terminal from Applications->Accessories->Terminal and type following three commands in turn:
sudo add-apt-repository ppa:gdm2setup/gdm2setup
sudo apt-get update
sudo apt-get install python-gdm2setup
The application will now update along with your other packages automatically and will appear in your System / Administration menu as “Login (GDM2Setup)“.