I have CentOS (64-bit) running and created a new Windows 7 VM using VirtualBox.  However, no startup it says this:
VT-x/AMD-V hardware acceleration has been enabled, but is not operational. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot. Please ensure you have enabled VT-x/AMD-V properly in the BIOS of your host computer. As a note, I am running Windows XP (32-bit) successfully as a VM.
			
			VT-x/AMD-V hardware acceleration has been enabled, but is not operational. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot. Please ensure you have enabled VT-x/AMD-V properly in the BIOS of your host computer. As a note, I am running Windows XP (32-bit) successfully as a VM.
				
		
			