From the homepage:
Prerequisites

To run DiscreteSIM you will need the Microsoft .NET Framework 1.1 installed. You can get this from Microsoft's web site.

What is DiscreteSIM?

Discrete SIM was designed as a proof of concept for a method of simulating the operation of discrete logic arcade games. Since these machines did not have a CPU and ROM code it's hard to simulate these machines using traditional emulation. Pure functional simulation of these games is also error prone especially since most people do not have access to the original hardware to compare against.

The approach taken by DiscreteSIM is to simulate the game circuit at the component level using a generic digital logic simulator. This allows the node list of the original circuit derived from the schematics to be input into the program and then simulated to see the video output and game mechanics.

Unfortunately the component level simulation is takes a lot of processing power so even on a very fast PC it probably will not produce a playable frame rate. On an AMD Athlon 64 3000+ system it takes about 8 seconds to render each frame.

Get it here:
http://atarihq.com/danb/Pong.shtml

-Trebor