Mac OS X inside Mac OS X

[dnlopes]

Hey,

I'm currently using Mac OS X 10.8.2 (Mountain Lion).
I need to run a double Mac OS X: one native and one with VirtualBox.

I've been trying really hard to get this to work, but I've not been successful.

I've already tryed with .dmg file and with .iso file, I've tryed with EFI checked, with EFI unchecked, etc...
Nothing seems to work.

Can anyone help me? What do I need to do to run Mac OS X inside a Mac OS X?