This is the full FX test that this technique was originally used for.

Before doing any shot like this (as with most shots), the most important thing is to plan it out first. You have to visualize what you want the effect look like and break it down from there. In this example I am going to use myself as an actor cloned 3 times and peeking out from various spots behind a doorway. And, finally coming through to chase everyone away with a lightsaber.

This tutorial will assume that you have at least intermediate knowledge of After Effects and the terms associated with it.

Now, please understand, I've never written a tutorial before. I really tried to be as detialed and specific as possible. But, some may still find this confusing. Please feel free to shoot me an email if you have any questions or suggestions that could help clear this up.

I've also made it a point to include a version of the After Effects workfile so you can see what the final clip should look like.
You can get that here: Download Example
The example includes really low resolution versions of the video clips in MSMPEG 4 CODEC. It also requires After Effects 5.0. Make sure you have both those things.

If you do not have the MSMPEG4 CODEC, Click here to download it.
Instructions: Unzip into an empty directory (no spaces in the directory name), Right click on the file named "MPG4VKI.inf", click on Install.

I sincerely hope this is helpful to you!!

Let's get started: Gathering all the parts