Typically, the file ~/.xinitrc decides which WM to start when you type 'startx' from the CLI. Mine is like this:
# exec fluxbox
In this case, kde is started because fluxbox is commented out. You can only have one uncommented entry here. Try adding:
to .xinitrc and see if it woks for you. The actual name of the windowmaker binary may be different...and that's what you need here.