I have latest generation Macbook Pro 7.1 (Intel Core 2 Duo) running Mac OS X 10.6.6. I installed Virtuabox 4.0.2 and tried to boot Ubuntu 10.10 64-bit iso. The boot options screen from the live CD came up:
However when I continued to load the live session, or installer for that matter, I encountered the following error:
This kernel requires an x86-64 CPU, but only detected an i686 CPU. Unable to boot - please use a kernel appropriate for your CPU.
I am not sure if VT-x is enabled or is supported in the Core 2 Duo of my Macbook Pro. But at least, I have both I/O APIC and VT-x enabled for hardware virtualization as told in the Virtualbox manual.