It wasn't a VirtualBox limitation, but an OS X... I know that VMWare won't let me create a VM of 10.6 unless it is from 10.6 Server install media.

How to install the virtual machine Open VirtualBox and choose Machine/New then choose a name for the virtual machine. For our installation, we will call it QubesOS-vm.

Yosemite is finally live! Here's how to get it, how to install it, and what you should do first, just in case.