I agree with all of the above statements, but particularly Post 4. If you can be confident that you know more, or as much about your topic as anyone in the room, there is no reason why you shouldn't feel confident. The key, then, I think, is research. Practice is important too, but I have always found that the best speakers were the ones who convinced me that they knew what they were talking about.
I think that the best way to overcome nervousness is to know what you are talking about. Knowledge is what gives us the confidence to give a speech. If you think about this, you will realize that you have no difficulties at all telling people something you know a great deal about. The same is true for public speaking.
The best way to control yourself is to practice a lot. Practice in front of the mirror and in front of family and friends. It's also good to choose a spot on the back wall to look at. People will think you are looking at them.
One should be sure that they are aware of who his or her audience is. That said, he or she should also be aware of the overall feeling of the audience. If a presentation is being given on a controversial subject, the audience will (most likely) include proponents from both sides. Therefore, the speaker must do everything possible to insure that he or she is not being offensive to either side. That said, one does not need to change his or her own prospectives in order to satisfy an audience--just be respectful.
As for how to control the voice and confidence, this is all about relaxation. As a student, I had a very hard time speaking in front of people. My hands would shake and my presentation would be filled with vocal pauses ("ums" and useless words). I had to learn to control my insecurities and fears. It was really only through forcing myself to calm down that allowed me to speak confidently in front of others.