IIS, PHP and HTML

Greetings All, I am at a new Gig. So this is the existing setup so changing it at least in the short term is not an option. We are in an IIS shop. We have a bunch of files that are html, and in need of php functionality. And that would be a BUNCH of files. I am interested in setting if I can set up IIS to use the php interpreter on HTML files. And then just start using the html files as php. There are just so many html files I would prefer to not do 301 redirects, not header redirects and blot the server with empty files (nearly empty). My preference is to use the existing files. Is there a way to make this happen? Are there any pitfalls in making this happen that I will need to be aware of? Blessed Be Phillip