The Mathematica applet is below which can be run in the browser. Mathematica free CDF plugin is required to.
The plugin can be downloaded from the Wolfram research web site http://www.wolfram.com/cdf-player/
This Demonstration illustrates the use of discrete distributions in Mathematica 6. Select the distribution from the menu, then select the values of the parameters by using the sliders. That updates the PMF (probability mass function) and the CDF (cumulative distribution function).