It's a great addition to your Halloween decorations!
Watch the video for the overview. (The camera can't do this illusion the justice it deserves.)
Step 1: Supplies
1. A piece of glass.
The size of the glass is relative to the size of the area where the illusion will be viewed.
2. A monitor (and computer, of course).
Either an LCD or CRT monitor will work. CRT monitors tend to give a better reflection, but an LCD monitor can be used in a much smaller spot.
The LCD monitor I used had a removable stand. That made it much easier to hide in the cabinet.
3. Floating head movie.
I recommend Big Scream TV.