You have not told that you are using PHP installer or trying to install manually,
If you are using installer than no problem, If not than try to use installer, Its best for beginners,
After installing you can find the php.ini file in system32 (C:\WINNT\system32) directory, where you can make any changes that works, and remember that after making changes in php.ini please restart the IIS to take effect.
Sorry for my bad english,