When installing on 10.4.8 the installer screws up
/System/Library/LoginPlugins/BezelServices.loginPlugin/ . This plug-in is read during startup just before the login dialog is shown, al least if you require pwd authentication. (To see where the system fails, press command-v at startup, after the chime, to unhide the console.)

Solution if your computer can start in firewire target mode. and you have access to a working mac running the same os.
1. Start the corrupted mac in firewire target mode (hold down the t key when turning the power on).
2. Connect the corrupt mac to the working mac using firewire. (Start the working mac if not started.)
3. Wait for the corrupt mac's disk to be mounted as a removable firewire disk on the working mac.
4. Start Terminal.app on the working mac.
5. In a terminal window, isse the command:
cp -r /System/Library/LoginPlugins/BezelServices.loginPlugin/ /Volumes/[corrupt_mac_name]/System/Library/LoginPlugins/BezelServices.loginPlugin/

This will replace the defunct plug-in with a working one. At least it did for me.