Nested Lab - Intel VT-x issues

Hello,

I'm trying to install a lab at work on our 5.1 production vCenter for VCP study and I'm following this excellent article: http://boerlowie.wordpress.com/2011/11/30/building-the-ultimate-vsphere-lab-part-1-the-story/

All has gone well until I tried to fire up the Windows2008R2 base image via VMware Workstation 9. I'm getting the following message:

However, the host is definitely a 64bit VM:

And the hardware is most definitely 64bit as this is our production environment. VM Machine version is 8 as per the instructions.

I've tried adjusting the Virtualisation Engine options to Intel VT-x on both the Workstation 9 options and on the host VM itself but I'm not getting anywhere. Am I trying to achieve something not possible here? Is it one virtual layer too many?

Thanks