1. aspnet_isapi.dll : this dll made for receiving request from browser. the dll normally accepts request from all the following mapping files.
.asax ASP.NET application files. Usually global.asax.
.ascx ASP.NET user control files.
.ashx HTTP handlers, the managed counterpart of ISAPI extensions.
.asmx ASP.NET web services.
.aspx ASP.NET web pages.
.axd ASP.NET internal HTTP handlers.
.svc WCF service
2. inetinfo.exe : In IIS 5.0 there is only worker process to deal with asp.net based request. the file may be located at C:\WINDOWS\system32\inetsrv\
3. aspnet_wp.dll : this is the worker process of asp.net pages, this is basically http runtime environment which process the page and send the response back to browser in the form of html.