Don't do what Schiffi said.
That will boot you up as root, and is primarily used for troubleshooting (doing fsck etc.)
What you want to do is in the login window, enter >console and no password. That will give you the console, and you can log in and have the full screen a terminal. (No Aqua overhead or anything.) This is much, much safer.
To save time, you can always make a new user with the name >console, so you don't have to type in >console.