With the free Virtual Box virtualization software you can run Windows Vista on your x86 Mac or even Linux on your Windows machine. Why would you want to? Because you’re an intrepid explorer of course. silly.
VirtualBox has an extremely modular design with well-defined internal programming interfaces and a client/server design. This makes it easy to control it from several interfaces at once: for example, you can start a virtual machine in a typical virtual machine GUI and then control that machine from the command line, or possibly remotely.