I know that this is possible, I've seen it done, but I've forgotten the command.  Basically, what I want to do (for various reasons) is to spawn a GDM/Gnome/etc session (a new one) from within my current session.  I don't want to use another tty. I want it to be windowed, and appear under my current session, so I can easily Alt+Tab, start/stop the session easily.Ideally I'll be able to do something to the effect of: <command> /path/to/gdm
Spawning GDM/Display manager within already existing X11 session
linux;xorg;x11
Possibly xnest or xephyr - these both let you start up an X session in a window.