Re: Unmanaged screens; GNOME Desktop is an X11 window manager. Window managers are X11 applications that manage other X11 application windows. However, Apple's port of X11 to Aqua implements its own window manager, so all X11 applications that are started on OS X will automatically be assigned to that window manager; there aren't any unmanaged windows for GNOME to manage. I don't know why you're trying to use GNOME, but if it's for its window management interface, you'll have to search for information on how to replace Aqua with X11 (which means losing the OS X Aqua-based applications); if it's for a particular X11 application set, you may still be able to use the applications with Apple X11; but you certainly won't get quite the same "GNOME experience".
Re: "The Settings Daemon restarted too many times." The Settings Daemon is trying to start, and failing quickly. Check the Console Log and see if there are any explanations within it. Also check the GNOME documentation and see if there's a way (there probably is, somewhere) to start the Settings Daemon manually; try starting it from an xterm window, that may yield some illuminating error messages.