Due to license restrictions the Mac OS X as Guest feature is only available to users with Apple/Mac hardware. Any other combination is unsupported and will therefore not work. Any post that talks about a different combination will be removed without warning. Any discussions of ways to get around the Apple SLA will also be removed.
At this time VirtualBox is not officially supporting the Mac OS X operating system as a virtual guest and there is no time-line when it will be officially supported.