From the Sun site when ready to download xVM VirtualBox 1.6: "Please note that the package architecture must fit your host operating system architecture. So if you are running a 32-bit kernel on a 64-bit capable CPU you have to install the 32-bit version (x86/i386). On the other hand you must install the AMD64 version (this is the same as x86_64) if your host kernel is 64-bit!" Is Leopard's (the host) kernal 64 bit or 32 bit for the purposes stated above? I am curious because I'm wondering if I should try to run Ubuntu 8.04 64 bit or 32 bit on my 15" Penryn MBP with Leopard as the host. Anyone else done this or have any tips, especially with Sun's xVM VirtualBox running Ubuntu?