virtualbox.org

VB 4.0.12; Host Windows 7 Ultimate.
Installing Windows 8 Beta I get as far as 'Windows Developer Preview' then comes the flashing black screen with 0xFFFFFFE6 error messages.
Do I need a BIOS with Hardware Virtualization Technology or just a later version of Virtual Box?

The first thing you need to do is update to Virtualbox 4.1.2. AFAIK no one has been able to get it to run in anything earlier and 4.1.x

I have hardware VT enabled but I don't know if it makes a difference.

Hardware-V is required to run W8 in VB. See http://forums.virtualbox.org/viewtopic.php?f=2&t=44577 for the whole discussion around W8. Please continue there, so everything is packed in one place.