Hi I have a new mac with Mountain 10.8.2 on it and I just installed Snow leopard 10.6.8 onto an external hard drive using my old mac to do this. Snow leapard on the external drive boots fine on my old mac so I installed it correctly BUT when I plug it into my new mac with Mountain lion and hold the option key it shows me the external snow hd I click to boot from it and nothing happens. The screen sits on the apple sign forever. PLease can anyone help me to be able to boot snow and run it on my new mac from the external drive. Thanks