TIP_Standard_Window_Manager

The use of this?

If you create several users and have only one window manager or want to set one by default because mosts users want that one or for any other reason. It would be very nice to just set this once in stead of creating a script or setting it yourself every time you create a user.

Get the X-session

To get a list of all the session you can start, check for the files in /etc/X11/Sessions. Now you for example see

Xsession kde-3.5 gnome

Here you pick the one you want to be start on default when a user types startx.

Conf.d

Open /etc/conf.d/xdm with you favorite editor. Scroll all the way down till you see

#XSESSION=

uncomment this and enter the ssession you chose above.

For example if you want to start kde-3.5 by default make it:

XSESSION="kde-3.5"

FAQ

Can a user change his default window manager? 

Yes, a user can still specify a personal Xsession through ~/.xinitrc