If VirtualBox is not showing 64-bit Operating System, Enable Hardware Virtualization or Disable Hyper-V. More suggestions are here in this post.

VirtualBox is flexible enough to handle many types of 32-bit and 64-bit configurations. If you need to run a 32-bit version of XP in a 64-bit host, you can do that without any problems.

VMware has a press release on their website that announces the release and availability of version 3.0 of Fusion, which brings 64-bit support along with other enhancements to the software.