1. You can install Snow Leopard directly. Any machine-specific files are integrated into the next main release, so if the white Macbook came with something less than 10.6, 10.6 has all you need.
2. If you install from the same computer but onto an external drive (USB or Firewire, even target disk mode should work), I can't see that there is any difference at all. Installing on another Intel Mac that came with something less than 10.6 originally should also be fine. Anything other than that and I'd be wary.