Your getting a 500 error which is internal failure message.
"I don't understand what is the expected response in a standard PHP installation."
Your PHP installation is not working and needs to be configured or permissions set correctly.
If you check the IIS Net Learning Center there are guides to get the PHP installation working.
If instead of the script you have in your post
use this in the test.php.
<?php
phpinfo();
?>
The script above should display information about the PHP installation,IIS Server and Windows.
If you have errors or it fails to display you need to fix have php.ini ,FastCGI , IIS Handler & Mapping or permissions .
If the script fails then you can use the same test.php script but test it at the command prompt.
To use php at the command prompt using the Start Menu open Run then enter CMD
and the return key you should see this >cd C:\Inetnetpub\wwwroot\ <-- Type this to change to the directory of
the IIS Server this is where the test.php should be then at the >php -R test.php <-- type this to run the test.php script page
the command should have displayed html text information for PHP installation,IIS Server and Windows.
If the command prompt test fails you need to fix problems in the php.ini file.
rahul