I realize that this isn't a conservitive topic, but I could use some help. My automatic garage door opener is dead. I want to replace it myself, but have never done this before. So, should I: A. dive right in. (some hints and tips would be great) B. have Sears do it. I also don't know what the difference between (good, better, best - etc.) chain drive, screw drive and belt drives are besides the price and the blatantly oblivious. Some help here to would be great. Any help or "It happened to me" stories would be fine. I can't...