This is my take/an update on las_vegas' hint I found here awhile back for running OS updates without creating a user on a Mac. It is applicable to any system 10.5 and up.
This can be helpful if you have a Time Machine backup that's on a newer OS than your install media, or if you're selling/donating your Mac as it saves the new user having to update things.
First things first, wipe your drive (and zero it if you don't trust the end user of this computer) and reinstall your desired OS.
Once your OS is installed, boot to your install media or the Recovery Partition if available. Open Terminal from the Utilities option in the menubar. In the new Terminal window, type the following:
This will bring up the Password Reset utility. Click Macintosh HD or whatever your HDD is called. You'll notice the only user account that's avail ...| Read more »