As promised, here is a video tutorial of how to create a simple virtual manipulative in GeoGebra. You can watch the embedded video below, or follow the link to a higher quality version on my site.
Link to video: http://plaza.ufl.edu/youngdj/geogebra_tutorial/geogebra_tutorial.html (Full Quality 5Mb Flash movie)
Link to the java applet created in the tutorial: http://plaza.ufl.edu/youngdj/geogebra_tutorial/linegraph.html
