I've recently discovered how cool it is to explain something using screencasts. They're a lot quicker to make than writing an article, a lot more efficient at explaining specific procedures and concepts and IMHO are just plain more enjoyable to follow. Recording these is also a great way to practice one's diction and “thought accuracy”.
I use the Canopus TwinPact 100 scan converter to capture the screen (neat box, rubbish software) which makes it possible to also cast stuff like installations and fullscreen apps.
While in installer mode, OS X always spans, not mirrors the screens (unless ofcourse the hardware is not supposed to support it). Pushing F7 doesn't do anything and I was already giving up on the idea, but then tried re-connecting the MiniDVI/VGA adapter (on a MacBook) and voila the screens were mirrored (to the lowest common resolution) and all was well!