Here's a simplified diagram outlining the steps IIS takes to process HTTP requests.
This shows the path an initial request takes and is very informative. Could you also post a picture with the flow of subsequent requests.
Nice attempt to visually document the request flow! It shows the flow when http request arrives but there is no worker process started yet to handle it. The sequence is not exactly happening the way outlined in the diagram above (from 12/16/2008). Tom is going to update the diagram later.
For easier understanding it would be better to show 3 diagrams. One diagram for service startup when W3SVC configures HTTP.sys with information about sites and app-pool mappings. Second diagram for processing first HTTP request when worker process to handle requests is not yet available. The third diagram for the simplest case when worker process is already running when request arrives.