Great introductory AR tutorial found at http://www.marcpelland.com/2009/03/26/getting-started-with-augmented-reality-flartoolkit/
What is Augmented Reality?
Augmented Reality is a technology that allows you to superimpose images into real-time environments. For the purposes of this tutorial, you just need to know that it reads a marker (shape/symbol), interprets the angle and size of that marker and then allows you to place objects at that size and position on the screen (or whatever your medium is).
Here are a couple example videos:
Mini Video and the GE Site
What is FLARToolKit?
To start with ARToolKit is the development package that has allowed developers to tap into the power of Augmented Reality. FLARToolKit is an Actionscript 3 port of the Java version of the toolkit.
What do I need for this tutorial?
In this tutorial, we are going to use FLAR Manager, which is a framework setup to make the combination of Papervision 3D and FLARToolKit easy and quick to setup/use.
If you would like to simply use FLARToolKit (or just get a little more information about it) clik on the following link: http://www.libspark.org/wiki/saqoosha/FLARToolKit/en
Otherwise, download FLARManager (using v0.1 in this tutorial) from http://words.transmote.com/wp/20090309/flarmanager-v01/ . FLARManager actually comes with a build of FLARToolKit in it and you can get it for AS3/FP9 or AS3/FP10 (we are using FP10).
You will also need FlashDevelop or another Actionscript editing tool. In this tutorial I am going to be compiling my code directly from FlashDevelop, but feel free to use the compiler/method of your choice.
You should also get a pattern generator so that you can create your own patterns (markers). Go here for more details: http://www.squidder.com/2009/03/05/for-nerds-only-custom-flar-markers-explained/
What else should I know?
You should be aware of the fact that there is a licensing fee to use check here: http://www.hitl.washington.edu/artoolkit/license.html for more details.