|MadSci Network: Engineering|
The demonstration you describe is indeed an impressive one. I once saw a similar, but even more impressive version of essentially the same effect. It was done on the last day of our sophomore college physics course, when we had learned enough to understand what was happening. This is a demonstration of electromagnetic induction, which is the effect that makes electric motors work. The professor charged up a large capacitor. He had an aluminum disc with a hole in the center, which fit around a large induction coil. The professor closed a switch, and the capacitor rapidly discharged through the induction coil, generating a large transient magnetic field around the coil. The aluminum disc (which had been cooled with liquid nitrogen to reduce its electrical resistance) shot up and hit the ceiling of the lecture hall! This device is a form of the rail gun. The ability of the rotating aluminum disc to support a permanent magnet depends both on the rotational speed of the disc, and also on the ratio of magnetic field strength to weight of the magnet. Thus, without knowing the type of magnet being used, it is not possible to say what is the minimum rotational speed which is needed by the disc. The demonstration you saw on NOVA probably used a NdFeB magnet, or some other type of high performance magnet. These rare-earth alloy magnets have been developed over the last 20 years. If you try to repeat this demonstration with an ordinary iron alloy magnet, it probably won't work. So perhaps you are too old to have seen this done when you were in grade school.
Try the links in the MadSci Library for more information on Engineering.