how to change default X login manager?
 

I tried to change it in Control Panel's Window Manager, but it doesn't take any change after I restart my X, the login manager is still Gnome. how to change it to kde?thanx

well the login manager (which are all horrible things IMHO) is defined by the default window manager you are using. if you have a skim though /etc/X11/prefdm (i think) then you can see that it will depend on the contents of /etc/sysconfig/desktop if it is manually specified, if not it should fall through that section to the if block beneath which just sees what it can find. set the DESKTOP or DISPLAYMANAGER variables in the desktop file, or if you want to be more hardcore and living on the edge, manually edit the prefdm script to point directly to the one you want. not that advised though!

Whenever I change my desktop/window manage is go to the command line and run xwmconfig.

run switchdesk as root and choose what is to be your default window manager.

I have tried this but the login manager is still gnome

Are you trying to change GDM to KDM (the screen that pops up asking you your username and password) or the actual windowmanager that starts once you logged in?

GDM to KDM