What's a podcast? Simply put, a podcast is a multimedia file that can be downloaded to your MP3 player or computer. PopSci's podcasts are like little variety shows, complete with music, informative interviews, and sometimes even photos and video. Each week, we'll talk to experts about the stories shaping the future of technology, from the frontlines of the "wired" war in Iraq to San Francisco's plan to turn dog droppings into electricityand everything in between.