RE: Diaphram Call
Like r33h said, practice, practice, practice! Some people can pick up a diaphragm call and work it without much practice at all. I consider myself a lucky one when it comes to mouth calls. I caught on pretty quickly. I had the DVD's and they really taught me a lot. Try practicing with your teeth together. Say the word "chuck". When you start getting sound out of the call, start saying the work "chee-uck".
With a little practice you'll be proficient with the mouth call. They're like riding a bicycle, once you learn you'll always know how. Also, try Youtube or some other video hosting site. Search for videos that show you how to work a diaphragm call. You'll learn a lot from videos.