Just a quick note on the CMPXCHG16B VirtualBox issue.
It's supposed to be fixed, according to https://www.virtualbox.org/ticket/11899.
But as of Mar 2014, when installing Windows Server 2012 R2 guest, on VirtualBox 4.3.8, on a Windows 7 64-bit host, it still failed very early in the initial boot process with the 0x000000C4 error.
I still needed to run the following command
"C:\Program Files\Oracle\VirtualBox>VBoxManage setextradata VM_name VBoxInte
where "VM_name" is whatever your VM is named as.