The downloaded file is an ISO.
Sometimes, users have allowed some 3rd party app (like WinRAR) to grab the .ISO file association, and in conjunction with the idiotic MS default setting of not displaying known file types, have been deluded into thinking the download is a zipped package and have unzipped it.
You must not process the download in any way.
Just set folder options like this and you should see the download as an iso. Just burn it whole and untouched.
If you cannot access the native W7 ISO burner, use Imgburn. It's free and it works.