I would like to install a minimal 64bit Ubuntu 12.04 server virtual machine to basically be able to use a terminal to run 64bit code alongside my 32bit Ubuntu 12.04 gnome session on my 64bit virt-enabled laptop. Where can I find the installation instructions for the best option to achieve my goal? VirtualBox? VMWare? Something else?
VMWare Player (or Workstation)
From personal experience, I can tell you that VMWare Player will almost certainly work for you, given that you have this scenario:
Try VMWare Player, and it will let you know what the problem is if it can't do what you want. (I couldn't find official instructions with a quick Google Search.
Virtualbox also has a similar feature since version 2.1, with similar requirements. From Chapter 3 of the Virtualbox manual:
Hope this helps!