If you mean 'how do I stop the X server from running, so that all I am given is the command prompt', then that is easy. Log in and press <CTRL>+<ALT>+<BACKSPACE>. If this doesn't work, then log in, open a terminal session and type init 3. This will close everything to do with X.
If you're running Mandy 8.1 and you want to stop X from starting, then you can run Mandrake Control Centre, go to the 'boot options' bit and unselect the 'start x on boot' option. There is a way to do this by editing a file, but I can't remember which file it is.