It is possible to have multiple operating systems on a machine, for that, you need a tool like rEFIt. It allows you to select which operating system you would like to start up on your Mac. It is only compatible with machines that embed Intel or that can work with EFI or Extensible Firmware Interface environment. To use it, it is necessary to install at least two operating systems first on the machine. It is compatible with Linux, Windows XP and Mac OSX.