How can I tell how many client computers are connected to my Web server?

Use the Web Service and Current Connections performance object. This counter measures the current number of active connections to the WWW service.

Open Performance Monitor: (Click Start -> Settings -> Control Panel -> Administrative Tools -> Performance)

1. Right-click the graph, select Add Counters
2. Change the Performance Object to "Web Service"
3. Highlight "Current Connections"
4. Click OK