Unless it's just a simplified example for the question, my advice is that drop the batch wrapper and schedule PHP directly, more specifically the php-win.exe program, which won't open unnecessary windows.
Program: c:\program files\php\php-win.exe
Arguments: D:\mydocs\mp\index.php param1 param2
Otherwise, just quote stuff as Andrew points out.
In older versions of Windows, you should be able to put everything in the single "Run" text box (as long as you quote everything that has spaces):
"c:\program files\php\php-win.exe" D:\mydocs\mp\index.php param1 param2