How to change login manager?
 

I recently installed a program called LTSP from ltsp.org which allows me to boot a diskless workstation off my server. After installing, however, the login manager has been reverted to the xdm manager (the ugly, non-user friendly one), and I want to be able to change this to the gdm login manager, although I am also wanting to run KDE for the session.

I manually forced KDE to start by modifying the value in /etc/sysconfig/desktop from GNOME to KDE for the time being, but I want my gdm login manager back!