Service Pack 1 for Windows Server 2003 has very detailed diagnostics information built in. With Trace Diagnostics, you can effectively use these diagnostics built-in by monitoring the requests to an IIS web server in real-time, or, follow a request throughout the IIS processing pipeline to find failures.
Included in this download are three individual tools:
1). Request Viewer
Microsoft, Windows Server 2003, Trace Diagnostics, Tool