Step 3: Display Setup
The goal is to make the background as dark as possible. Play the movie you want to use full screen, then adjust as needed.
For the cabinet configuration, suspend the LCD monitor above the viewing area. Then create a Halloweenish looking scene inside, and then place the glass over it at an angle that will reflect the image to the viewer.
For the windows configuration, set the monitor on the floor pointing up, create your scary scene, then place a much larger piece of glass over it at an angle that will reflect the image towards the window.
In either setup, the bottom edge of the glass should be as close to the bottom edge of the monitor as possible. That will make the image float in front of your scene, instead of behind it.
Adjust the angle of the glass to control the height of the floating head.