do you want it to boot in text mode all the time or just when you tell it to?
If you want to change it for good go into the etc directory and open the file inittab
change the line
CODE
id:5:initdefault:
to
CODE
id:3:initdefault:
if you ever want to change it back, just change the 3 back to the 5.
If you want to change it just for a specific boot you can just ad the line id:3:initdefault to the grup boot order and boot it.
That should do it for you. Make sure you don't typo or you will be in a heap of trouble.