A new beta build of VirtualBox, Sun’s Oracle’s free x86 virtualization software, makes it possible to run Mac OS X as a guest operating system…no shenanigans or flaming hoops to jump through, just pop in the $30 retail Snow Leopard upgrade disc and go. This had previously only been possible with some awkward Hackintosh-style maneuvering, or using recent editions of commercial virtualization products.
At this early stage, performance is fairly sluggish, the screen size is fixed and there’s no sound support, but the OS otherwise appears to run feature-complete (including networking and USB). Hopefully future builds will ramp up to the level of functionality and performance that VirtualBox provides for other guest operating systems.
Installation tip: when you come to the step prompting for a target disk for installation (which will likely show no available volumes), run Disk Utility from the “Utilities” menu, format the virtual disk image you created when setting up the VM (Mac OS Extended, Journaled), then exit Disk Utility to return to the OS X installer. You can then select the newly-formatted virtual disk and proceed with installation.