How is it that PHP works on an Internet Information Server (IIS)???

Did Microsoft include code in their IIS 6 and 7 that handles PHP. If the answer is yes, why would Microsoft do that? Or, did I miss something here? I know that I've installed PHP 5.3.x on my Vista Machine and I use IIS 7.0 on my Vista machine as my web server, so is the PHP 5.3.x working with IIS to serve up PHP pages? Do IIS and the PHP program somehow work together?