Coding PHP on Localhost

Im trying to get my PHP-based site working on localhost before I upload. I am running Windows and I have configured IIS for using php.

If I try to open it using http://localhost/page.php, IE thinks its supposed to download the php file instead of showing the processed page from the server.

This is weird because I can load any other php file from the same localhost and it works, which means that PHP is configured correctly. Also site seems to open if I run it under EclipsePHP.

Any ideas?