Also, be sure to see Antonio Carlos M. de Queiroz's website http://www.coe.ufrj.br/~acmq/electrostatic.html, and also the Yahoo group VanDeGraaffGenerator, where he answers all kinds of questions.
Not wanting to hi-jack scieng's thread but this may help him also.
Why do some plans for a Van der Graff show a high voltage "sprayer" use on the lower belt pulley? I always thought a Van der Graff was strictly a static/friction generator. Any one know?