So, I am loving my MBP and OSX. I want to back up my HD, particularly my iPhotos. I have an Airport Extreme with a 1 TB external hooked up to it. How does the time machine work? Will it back it up on a regular basis? Can I set the schedule? Does it just keep (1) copy of a back up and write over that each time it backs up? Sorry for the noob questions? Thanks!