I've been told it's not possible to use a USB drive to boot from and I've read that it can be done on a few different websites. I have the .dmg Snow Leopard file on the external USB HD and want to upgrade my MBP. I pulled the dmg file from the DVD using another computer. My DVD drive is not working on my MBP and I was hoping to find a way to upgrade without it. Every time I try to put a DVD in, it sounds like it is trying to read it but eventually just spits it out over and over. Can I do this and if so, what do I need to do first to prepare for it (partitioning and such)? I've never done anything like this so speak to me like a child!