How can I boot into the console?

What used to work (I've not tested it on recent O/S versions) is:

1. Open System Preferences->Accounts->Login Options
2. Select "Display login window as:" 'Name and Password'

Then, for the User name, enter >console

If you want to come up in Single user mode, you do it with the 'Command-S" combination while booting.

If however, you want the system to always boot automatically into console mode---I'm afraid I can't help you.

This is on 10.6.2, but 10.5 seems to be identical

#
# @(#)ttys 5.2 (Berkeley) 6/10/93
#
# name getty type status comments
#
# To secure single-user mode, enable Firmware password protection.
# http://docs.info.apple.com/article.html?artnum=106482
#
#console "/usr/libexec/getty std.57600" vt100 on secure
console "/System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow" vt100 on secure onoption="/usr/libexec/getty std.9600"
#tahoe's only
#remote "/usr/libexec/getty std.1200" pt on # diagnostics
# The tty.serial entry initializes the serial port (if any) for use as a
# terminal (enabling logons over serial). If marked secure, the serial
# port will allow root logons.
# To make the serial port available for outbound
# communications, the tty.serial entry should be turned off
# (set the 4th field to off).
tty.serial "/usr/libexec/getty serial.57600" vt100 off secure
# Fax reception is off by default, use the
# System Preferences panel to enable it.
fax "/usr/bin/fax answer" unknown off
# Hardwired lines are marked off, by default, so getty(8)
# is quiet when they don't exist.
tty[00-07] "/usr/libexec/getty std.9600" unknown off secure
# pseudo-ttys
ttyp[0x0-0xf] none network slot=36
ttyq[0x0-0xf] none network
ttyr[0x0-0xf] none network
ttys[0x0-0xf] none network
ttyt[0x0-0xf] none network
ttyu[0x0-0xf] none network
ttyv[0x0-0xf] none network
ttyw[0x0-0xf] none network
# cloning ptys
ttys[000-999] none network