This is something I was looking for after I moved from Linux to Win2k3. On Linux I have been using SIM. I'm going to give IISTracer a try this week.
http://www.pstruh.cz/help/iistrace/iis-monitor.asp
"IISTracer is a real-time internet web site monitoring tool for Microsoft IIS (all versions). The software lets you show what is happenning on IIS server right now. You can see or log state of each request, incomming/outgoing bytes, http headers and several request running times.
IISTracer shows a state of running script (.asp, .cfm, .php, .cgi, ...), applications (.dll, .exe, ..) and a big downloads (.mp3, .zip, ...).
It lets you also monitor what script or which client (IP) hangs-up your server.
You can stop long running requests (uploads/downloads)."
Best thing would be to use a third-party app to launch IISTracer as a service (Firestarter or something like that as far as I remember).
[EDIT]
There are performance tests if ISSTracer on their page too:
http://www.pstruh.cz/help/iistrace/2010.htm
AND:
You can access all IIS Tracer web site monitoring tool configuration functions and values from http interface using standard web browser.
Looks like one sweet util. Anybody already using this? Any comments?
[EDIT]
Anybody came across other useful monitoring utilities for Windows?