You've picked an OS!
As you don't know what Linux is, it's preferable to skip over to this section.
Oh, I see how it is. Windows only supports x86 CPU architectures (hence the popularity of it today), so if you want to port Windows onto ARM, Windows RT won't work, so consider editing ReactOS and make it ARM compatible. (If you know what to do, that is. :) It would be awesome to the community!)