This is a tutorial explaining Virutal Machine software, what VirtualBox open source software is, and a basic into on how to use it. It then covers how to create a new guest vm and install Windows XP.
Run Windows on Mac. Run Mac on Windows. Run Linux of Windows. Run Linux on Mac. Run Mac on Linux. Run Windows on Linux
VirtualBox is Open Source software, and is available to you for free. It is a great alternative to VMWare and Parallels.