If you have one windows partition and another for storage, and you want to replace  the first by Ubuntu's, it's not a straightforward install. I made it, but my father wouldn't.

As for Windows Manager, it's not Nautilus, but Gnome itself (or the default settings that come with Ubuntu). The window style, even the shortcuts  (like Alt-F4) are made to copy Windows' window manager. I understand that choice (to make the transition easy enough).