Basically my hard drive failed..... , no problem though. I have a time machine back up....but the external hard drive i have is not able to have leopard/snow leopard installed on it. It says "you cannot install Mac Os on This volume. Mac Os X cannot start up from this volume. I have tried formatting the external hard drive to a mac format but nothing has worked. What needs to be done so that i can format my external hard drive to boot snow leopard or restore from time machine?????? Thanks guys.