NT+IIS+PHP+authentication

I have : NT 4 server, IIS 4, PHP3 installed (I did not compile with vc++, i imagine it is called "CGI version of PHP") everything works fine! I want to add user authentication, so I open the security tab of a web directory (i.e. I remove full control for "everybody" user and I add full control for some users only) and this is what happens: - htm file are browsed with a pop-up username/password dialog box and it's exactly what I expect; - I cannot access all the php3 files (FATAL ERROR: ... not able to open ... no input file specified) Anybody knows what happens? Is it a IIS problem? FZ