Look at /etc/inittab near the bottom you should see the tty lines like this:

From my knoppix live cd session:
# <id>:<runlevels>:<action>:<process>
# 4 virtual consoles with immortal shells
1:12345:respawn:/bin/bash -login >/dev/tty1 2>&1 </dev/tty1
2:2345:respawn:/bin/bash -login >/dev/tty2 2>&1 </dev/tty2
3:2345:respawn:/bin/bash -login >/dev/tty3 2>&1 </dev/tty3
4:2345:respawn:/bin/bash -login >/dev/tty4 2>&1 </dev/tty4

These lines are from my debian woody system:

1:2345:respawn:/sbin/getty 38400 tty1
2:23:respawn:/sbin/getty 38400 tty2
3:23:respawn:/sbin/getty 38400 tty3
4:23:respawn:/sbin/getty 38400 tty4
5:23:respawn:/sbin/getty 38400 tty5
6:23:respawn:/sbin/getty 38400 tty6
either comment out the tty lines so you have no logged in terminals started up, or change them to getty lines like a stock linux would use.

rock