Today I read a question in one of the IIS.NET forums - although I'm not sure if this is what they really wanted to know - I figured it might be useful to understand how to do this anyway. Several times users does not like exposing their ASP.NET pages using the default .aspx file extension (sometimes because of legacy reasons, where they try to minimize the risk of generating broken links when moving from a different technology, to preserve the validity of previous search-engines-indexes and sometimes for the false sense of security or whatever).
Regardless of why, the bottom line, to map a different file extension so they behave just like any other ASP.NET page requires you to add a couple of entries in configuration, especially if you want those to be able to work in both Pipeline Modes "Classic and Integrated".
For this exercise lets assume you want to assign the file extension .IIS so that they get processed as ASPX pages and that you only want this to be applicable for Default Web Site and its applications.
Lets actually describe the AppCmd.exe lines since it breaks nicely the different operations.
Hopefully this helps understanding a bit how to re-map extensions to ASP.NET extensions, and in doing that learn a bit more about preConditions, Handlers and AppCmd.