What is an Expert System?

Whatis.com defines an expert system as follows:

After being an active Knowledge Engineer for 2 years modeling troubleshooters for various Microsoft products, I wrote a 70-page tutorial to train new knowledge engineers. On a later freelance project, I converted the Word document to a compiled online help format.

Microsoft has graciously given me permission to post the tutorial here: (No longer available, code originally written to run in Internet Explorer 4, and no longer works in modern browsers)