another option to work around this is to skip the brain-dead softwareupdate installer when it comes to Quicktime. This looks longer than it is actually. Once you have the files you need, you can copy the quicktime installer .pkg to whatever computers you're working with.

go to the Quicktime 'Standalone' installers page:

<http://www.apple.com/quicktime/download/standalone/>

Click on the 'download now' button and let the download begin. Download the file to the desktop (and if you're in safari and need to do a remote install ctrl-click on the download progress box to copy the download url... something like this:

<http://a1540.g.akamai.net/7/1540/52/20041101/qtinstall.info.apple.com/pthalo/us/osx/QuickTimeInstallerX.dmg>

then use the 'installer' CLI option

installer -verboseR - pkg /Volumes/QuickTime\ Manual/QuickTime652.pkg -target /

voila, no stupid serial number prompting. Sure saved me a 4000 mile trip to hit 'enter' on the keyboard of the machine I was working with.

Admittedly, this 'workaround' looks longer but it takes all of a few seconds to extract the necessary file once it's downloaded and then the install process can continue without unnecessary user intervention.

FWIW, YMMV