I get asked this question a lot as I go around demonstrating the benefits of using URL Rewriting in ASP.NET, how can I process wildcard extensions and just directories in IIS 6.0 on Windows 2003 and ASP.NET? It is very simple, but not obvious at all. This entry will walk you through configuring IIS to process all request through the ASP.NET engine.
The first thing you must have is access to the IIS Management console and Administrator privileges to the web server. Once you have these things in place you need to open the properties dialog for the Web site you will be configuring.
IIS Web Site Properties Dialog
Select the 'Home Directory' tab. Once on this tab select the 'Configuration' Button. This will display a three tab dialog, the first tab, Mappings is what we are interested in. Notice the lower portion of the tab list 'Wildcard Application Maps', here we will want to add a reference to the ASP.NET engine. The easy way to do this is to double click on one of the ISAPI extensions in the top portion and copying the path to the ASP.NET .dll file. You will need to select one of the ASP.NET file extensions, like .ascx or .asax to do this. The path should look something like this: DRIVE:\%windows%\microsoft.net\framework\v2.0.50727\aspnet_isapi.dll.
IIS Web Site Configuration Dialog
Now that we have copied the path to the .NET engine we need to add it to the Wildcard mappings. Select the Insert button to the right of the mappings list. Now you will have an Add/Edit Application Extension Mapping dialog displayed. There are two pieces of information you need to supply, the ASP.NET engine path and uncheck 'Verify File Exists'. Now select 'OK' until all the property windows are closed.
IIS Wildcard Application Extension Mapping Dialog
Now all URL requests to the web site will be processed by ASP.NET no matter what the extension or lack of extension. Pay attention for my next entry on how to leverage this feature to map URLs without extensions to actual dynamic pages on your Web site.
Reference - Installing Wildcard Mappings in IIS 6.0