Yes, sort of. You can download Windows, but then you need to burn it to disk or USB. It requires this to allow you to boot to that disk when you restart your machine. Mounting the ISO to a partition might not work.
You can easily download the ISO version of Windows, and create the disk that way.
There's a whole article detailing the process here:
That article includes a tool that will let you burn the ISO to DVD or USB but it only works in Windows. If you're unable to use that tool, you will need to use your favorite burning software to do it.
OR if you're using Boot Camp 4, you might be able to use the Boot Camp Assistant to create this disk. Depending on your Mac, there might be an option for "Create a Windows 7 install disk". See here for info: http://manuals.info.apple.com/en_US/boot_camp_install-setup_10.7.pdf