There are two versions of the Macintosh graphical login screen; the first
one is default, and you have to go to the second to be able to switch to
console mode.

<p>
The first login screen shows user names and icons for each user; you click on
a user, and then you get a text box to enter the password.
http://www.osxfaq.com/Tutorials/console/7.jpg

<p>
If you press option-return and then click on any user icon, then you will
get to the second login screen, which does not divulge valid user names
but instead asks for username and password in two text boxes.

<p>
On this second login screen, where you can type text for "username", instead
of a username type ">console" (that's a greater-than sign at the beginning,
but you can think of it as an arrow -- go to the console).

<p>
An alternate possibility is to add a "user" named ">console", in the "users"
preference pane in System Preferences.  This odd user name will not be
loginable, but clicking on it in the first login screen will go to the text
console just like typing ">console" manually in the second login screen.

<p>
More drastically, you can make the macintosh boot up always in non-GUI
mode by editing /etc/ttys.  I believe that this also requires setting the
macintosh to boot in "verbose mode" (which is not harmful and is slightly
useful in any case) with "sudo nvram boot-args=-v".  In "verbose mode", you
get to see unix booting in a text console.  If you then edit /etc/ttys so as
not to start the gui login window but instead to run getty on the console,
you'll have a traditional unix text login.

<p>
http://www.eddav.dyndns.org/disabling_aqua.html