Windows Server 2003 provides an inherent ability to count and graph the number of active client connections to your server by using the Performance Monitor.
Open Performance Monitor by navigating to Start -> Administrative Tools -> Performance
Right Click on the main graph window, and choose Add Counters.
Under the Performance Options drop-down menu, choose the option for Web Service.
Leave the option for Select counters from list selected, and choose Current Connections. Once selected, click Add, and then Close.
The number of web users currently connected to your server will now be represented by a color-coded line graph.