It's installed in my Programs directory on the home disk. "Proper authorization" in Windows 7 is a nightmare, an absolute nightmare. I am not very knowledgeable about W7 as I am really a Mac guy and this is my first Windows machine. As for your first questions, I guess the answer can only be "I don't know", as I don't have displacement turned on, I have five lights in the scene, and I wouldn't know if any of the other settings are incorrect.

One thing I do know is that I simply can't have files that big filling up my drives. Since it crashes either way on this file I've turned the option on again. I've finished rendering the scene for the last time and I'm hoping not to have to load it again now.