I have a script that runs on my server and alerts me to available software updates.
Since 10.2.8's version of the 'softwareupdate' command line tool doesn't let you add/remove ignored updates (like 10.3's does), and since I don't feel like making my stupid script any smarter, I decided to install the QuickTime652-6.5.2 update.
Of course, like previous QuickTime updates, it stalls after printing 'Installing "QuickTime"... 50%' a few times.
A little checking and it looks like there's a perl 'preflight' script that is running and is stalled. Killing it aborts the install.
A quick read-through of the script reveals the secret:
(tcsh syntax)
%setenv COMMAND_LINE_INSTALL 1
Setting that variable will prevent the QT installer from attempting to show the alter/registration dialog and so the headless install can continue.