Before Window Maker can be used, each user must run wmaker.inst so the GNUstep directory is set up in the home directory. Additionaly, after you set up one users account, you could copy the GNUstep directory to /etc/skel so that each additional user created with useradd -k will have this information copied over for them.
If you call X from the command line, then you can edit ~/.xinitrc to automatically start Window Maker: exec wmaker If you are using xdm, gdm, or kdm, edit ~/.XSessions to include wmaker.