[gentoo-dev] Comparing Openpkg with portage

[m h]

Hello-

I'm investigating the similarities between portage and openpkg. More 
specifically I was wondering if it is possible to take portage and install 
in on top of an existing linux installation in its own sandbox (similar to 
what openpkg does). I've done some googling and found the documentation 
about the gentoo sandbox (http://bugday.gentoo.org/sandbox.html), but this 
seems to be a tool for checking that ebuilds behave correctly. I've read 
through the developer documentation and didn't find anything there. Google 
hasn't necessarily been very useful either....

So, is it possible to sandbox a portage installation on top of say a debian 
or fedora install? If so, can anyone point me in the right direction?
Do any of the devs out here have experience with openpkg?

thanks

matt