Total rookie here. Currently running Tiger. I want to do a clean install of Snow Leopard. I've backed up my hard drive to an external device. Before I wipe the slate clean, how can I be certain the external drive contains everything I will need to repopulate the new system? I'm afraid I'll start adding stuff after the install and realize too late that I'm missing some crucial permission or folder. When I look at the external drive finder, I see that I, the admin (God help us), don't have access privileges to many of the other users' folders. Does this matter?