how do I switch between two desktop managers?
 

If I install a new desktop manager without uninstalling the old one, how do I specify which one to use? I wanted to look at LXDE, so to see what would happen, I installed it without uninstalling KDE. KDE apparently just sat underneath, and was unaffected. I didn't keep LXDE, but I might, if I could switch back to KDE to do work until I understood LXDE. (Keeping up-to-date in MEPIS will force me to learn KDE 4 despite that KDE 3 was fine, so I might as well examine other desktop managers.)

Usually you just log out and then select LXDE from the Session Manager on the login screen.

The answer is the startup script.
 

IF your system starts with a session manager, it usually has a list of the available desktop managers. If your system boots straight in to a session, see the scripts in "/etc/X11/xinit". There is a script named "xinitrc" that actually initiates the X11 system with a given desktop manager. There can be a lot of scripts named like "xinitrc.kde", "xinitrc.fluxbox" and so on. The "xinitrc" script is a symbolic link to the default startup.

Additionally, you can set the default per user by copying any of the /etc/X11/xinit/xinitrc* to $HOME/.xinitrc

Okay, I successfully did that. I thought the options would be there in plain sight, but not quite: I had to click on "the session type" and select one. Thank you.

Since KDE has to be my default until I figure out LXDE, I'll wait until then to tamper with the X11 scripts or files.