I have a year old MBP with Snow Leopard. I don't have enough drive space to updgrade to Lion. I would like to install Lion on my external Firewire hard drive, and then have the space to install xcode etc.. I have heard it is possible to install and boot from an external drive with a Mac. I do have bootcamp with Windows 7 - so I hold option when booting to pick between the Windows and Mac installs. I presume if I could dl and install lion, it would show up as a third choice when booting with that external disk connected? TIA!