Instructions for locking down physical access to the Untangle kiosk:

First, follow jdelagarza's excellent post on setting up xscreensaver and test that it's working:
http://forums.untangle.com/feedback/...aver-lock.html

Unfortunately this can still be easily defeated using ctrl+alt key combos to restart X.
Answer:
1) build a good xorg.conf (see example below) so Xserver uses /etc/X11/xorg.conf instead of falling back to /etc/X11/xorg-untangle-vesa.conf (which is useless to modify directly as it automatically overwritten by /home/kiosk/.bashrc)

2) add a ServerFlags section with the following options:
"DontZap" to disable ctrl+alt+bksp and ctrl+alt+del
"DontVTSwitch" to disable ctrl+alt+F[1-12] (especially want to disable F10 which also kills X)
"DontZoom" to disable using ctrl+alt+[+/-] to crash X

3) reboot/restart X
My current /etc/X11/xorg.conf
Code:
# xorg.conf (X.Org X Window System server configuration file)
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg
#

Section "ServerFlags"
        Option          "DontZap"       "true"
        Option          "DontVTSwitch"  "true"
        Option          "DontZoom"      "true"
EndSection

Section "InputDevice"
        Identifier      "Generic Keyboard"
        Driver          "kbd"
        Option          "XkbRules"      "xorg"
        Option          "XkbModel"      "pc104"
        Option          "XkbLayout"     "us"
EndSection

Section "InputDevice"
        Identifier      "Configured Mouse"
        Driver          "mouse"
EndSection

Section "Device"
Identifier "Configured Video Device"
Driver "vesa"
EndSection

Section "Monitor"
Identifier "Configured Monitor"
  VertRefresh  60
EndSection

Section "Screen" 
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
DefaultDepth 24
SubSection "Display"
Depth 24
Virtual 1024 768
Modes "1024x768" 
EndSubSection
EndSection
You can verify which xorg.conf file the Xserver is using with this command:
# cat /var/log/Xorg.0.log | grep "Using config file"

Enjoy.