The way an ASP.NET request is handled by IIS is quite different in IIS 6.0 when compared with 5.0. In 5.0, the ASP.NET worker process is handed off control by the aspnet_isapi extension in IIS. The aspnet_isapi dll runs in the inetinfo.exe process in IIS and functions what is known as the CLR host (a CLR host is the piece of unmanaged code which is responsible for loading the CLR into the memory). So aspnet_isapi “hands over” the processing to the worker process named aspnet_wp.exe, where the request passes through a series of HttpModules and an HttpHandler.
But in IIS 6.0, there is a driver named http.sys which listens to all the incoming requests (aspnet_isapi.dll is not in the picture at this point). The moment an ASP.NET specific request comes in, this driver starts an IIS 6.0 worker process (which is not related to ASP.NET at all) named w3wp.exe. This process now loads the aspnet_isapi.dll (CLR host) and the request follows through a similar sequence of HttpModules and HttpHandlers.
So the important thing to note here is that w3wp.exe is not an ASP.NET worker process (unlike aspnet_wp.exe) but instead specific to IIS 6.0.