You can boot in runlevel 3 (text-mode) by changing the default runlevel in /etc/initab from 5 to 3:
Code:
# The default runlevel is defined here
id:3:initdefault:
For temporary change, you can add a plain '3' (or 5 resp.) to the kernel options in the grub menu (one of the F-keys will get you there).
To load the graphical system from runlevel 3, type 'startx'