If i'm trying to be selective, I install everything from X which will included a very basic window manager, then I deselect all the window managers under xap and choose the one I want.
EDIT, if you already have slackware installed and you need the space then you can remove the ones you don't need... Here is an attempt and listing them all
Code:
su -c 'removepkg blackbox fluxbox fvwm twm windowmaker xfce'
of course you could remove kde... but that may impact some of the programs you run that rely on some kde libraries.