how do I choose KDE or Gnome after instalation
 

I installed Slack9, and I want to switch between Gnome and KDE. How can I do this ? What file must I edit ?

Welcome to LQ :)

Assuming you are logging in through the terminal, use:
xwmconfig

To choose a different window manager. Otherwise, to do it by hand, edit:
~/.xinitrc

HTH

Cool

Thanks, and please tell me how to configurate Slackware to boot automatically in X ..

As root user in /etc/inittab change this line

id:3:initdefault:

to

id:4:initdefault:


ie change the 3 to a 4 then save and reboot