virtualbox.org

My host system is MacOS SnowLeo.
I've installed VBox v.4.1.6 and Windows XP SP3 Guest system
In that WinXp i've installed another VBox for windows.
I've made new Debian VM and started it up.
And there is a problem. System is starting very slowly. It hangs about couple of minutes on message:
"SPM alternatives: switching to UP code"
after that i've got kernel panic. (see attachment)

What is wrong? What can i do to start it right?

thanks

Nested virtualization is not supported.

where i can find info about it? is it official not supported or a bug?
is there is some work to support nested virt?
which virtualization software supports nested virtualization?