Microsoft Knowledge Base Article 313064 contains the following summary:
This step-by-step article describes how to create and configure counter logs in System Monitor so that you can monitor Web server performance.
In System Monitor, you can create logs to automatically collect server activity data at specified intervals. You can then use this data to help you identify the cause of delays, and to tune your server for optimal performance.
System Monitor uses counters to track the activity of specific objects (services or mechanisms that control server resources). In addition to the objects and counters that are included with Microsoft Windows 2000 Server, Internet Information Services (IIS) 5.0 installs counters that monitor Web server performance. These counters include global IIS counters, Web service counters, File Transfer Protocol (FTP) service counters, and Active Server Pages (ASP) program counters. Global IIS counters monitor the activity of all IIS services, such as bandwidth usage and caching. Web service, FTP service, and ASP program counters monitor connection activity.