Well, I'm not positive about the sound that you are talking about that Dime gets on "Walk". It might be a trem dive-bomb. Which is when you push the trem bar all the way to the body. It tunes the strings way down and gives a real loose, deep sound to the guitar. I'm not positive and I can't recall that song off the top of my head. Some other metalhead can help you out with that one. As for the question about distortion and overdrive.... the names basically say it all. Distortion is just that, a distortion in the sound. It uses the same basic tones but gives them a muddier sound. Distortion is a pertty versatile effect... you can use it in lead tones as well as rythm tones. Overdrive however makes the tone sound more "pushed". It gives the tone a sharper, tighter sound. When used in conjuction with each other you can get some pretty cool lead tones. Unlike distortion, overdrive can push your tones out front in a mix by running at a higher frequency... therefore overdrive is most widely known as an effect for lead tones.