The past few years have seen a rapid growth in the popularity of the Internet and the usage of the World Wide Web in particular. Thousands of companies are deploying Web servers and seeing their usage rates climb dramatically over time. Our research has focused on analyzing and evaluating the performance of Internet and intranet Web servers with a goal of creating a Layered Queueing Model to allow capacity planning and performance prediction of next generation server designs. Along the way we built a tool framework that enables us to collect and analyze the empirical data necessary to accomplish our goals. This paper describes custom instrumentation we developed and deployed to collect workload metrics and model parameters from several large-scale, commercial Internet and intranet Web servers over a time interval of many months. We describe an object-oriented tool framework that significantly improves the productivity of analyzing the nearly 100 GBs of collected measurements. Finally, we describe the Layered Qqueueing Model we developed to estimate client response time at a Web server. The model predicts the impact on server and client response times as a function of network topology and Web server pool size.