Debian defaults to 2, but if you installed gdm, kdm, xdm it will change it's default to 5. The 5th line down in /etc/inittab is the one you want to change. Make it 2 or 3, and then you'll be in business.
# /etc/inittab: init(8) configuration.
# $Id: inittab,v 1.91 2002/01/25 13:35:21 miquels Exp $
# The default runlevel.