HTTP API / http.sys / Sam talks about IIS6. The New Request Processing Architecture of IIS 6.0/Win2K3. [Sam Gentile's Blog]
Sam tells how IIS uses http.sys. My side note is that you too can use port 80 while IIS is running via the new Win2k3 Http API. ;) [Doubt's log]

Craig Andera asked "How can I take advantage of this to have my app listen on an arbitrary endpoint on port 80?" too. I guess this API is the answer.