Starting an XSession within an XSession
Start an XSession on another virtual terminal from within your current XSession.
gdmflexiserver
Start an XSession within the window.
gdmflexiserver -- xnest
The gdm stuff only works if gdm is your login manager. I want to figure out how to do similar things with kdm. Xnest is part of X and lets you run an Xsession nested in a window.