Apache has mod_rewrite; now IIS has a small, cheap (free) rewriting module:
Ionic's ISAPI Rewriting Filter (IIRF).
Specify rewrite rules using regular expressions.
An incoming URL like http://foo/bar/bam
can be translated into http://foo/baz/bam.jsp
ASP.NET has a URL mapping mechanism, but it works only for filetypes that are handled by ASP.NET: aspx, ascx, asmx, and so on.
For static files or non-ASP.NET files, (XML, GIF, JPEG, CSS), the ASP.NET mapping won't work cleanly.
IIS, like Apache's HTTP server, has an extension mechanism: it is called the ISAPI filter.
There are commercial ISAPI filters that endow IIS with the ability to re-write URLs. This is a cheap and powerful alternative.
The comments insply free and cheap - they sort of don't normally go together so it is hard to know - no publisher site was found.