Hosting ASP.NET in IE
The CodeProject article, "A Simple protocol to view aspx pages without IIS implemented in C#", is intriguing.
It uses a custom protocol handler (aspx:) that instanciates the ASP.NET runtime, sends it the request and reads the response back to IE, allowing to test aspx files without a web server.
The web.config and global.asax are searched back to the root in the file path.
There are some limitations like problems with cookies and mime-type headers. Also you probably need to be careful not to jump out of aspx: back to the http: protocol.
I'm not sure whether the HttpRuntime is instanciated at every request or if a trick is used to make it stay alive in the background (required to maintain session state).
Another article on instanciating the HttpRuntime for use on the desktop.