I've installed the ZEN Cart on a Windows 2000 Server with IIS 5.0 installed. I can access all files on the site except for the php files. I even created an html file and placed it in the cart folder. I can access that just fine. When I try to access /cart/index.php it asks for a username and password. I've already checked the security of the folder and also directory security in IIS.

Do you have any ideas what could be happening?

I know that PHP works because I am using it on some other sites on this box.