"Courage is not the absence of fear, but the mastery of it." - author unknown.
Anything worth doing usually requires a certain amount of risk. "Risk" is one of the many catalysts for fear.
Conquering a fear of public speaking can be accomplished by using the same principles that you would use to conquer the fear of most anything.
1.) Identify what it is exactly that makes you afraid of public speaking. Here are some common concerns that people fear: Is there something about my appearance that I don't like? Will I say something people will think is stupid? Is my voice clear and easy to understand? Will I forget something or loose my place in my presentation? etc. etc. etc. Personalize it for YOU! It may be one, or a long list. Whatever it is, once you identify it you will be able to work on overcoming it.
2.) Prepare your message carefully! There are many different methods to preparing a public presentation. Some people write it out word for word and then read it exactly as it is written from their notes. Other people will write an outline and then speak from their thoughts using the outline to keep them on track. Whatever method you choose your confidence will be much higher if you thoroughly know your subject matter.
3.) Prepare yourself mentally. For whatever reason, YOU are the person who is giving the presentation. Therefore, YOU have something important to say and the people in the audience are there to hear you say it. If you have done your research, practiced your delivery, and prepared your appearance to the best of your ability, then get out there and speak with authority.
These three thing are by no means all inclusive to conquering a fear of public speaking, but they should help you get started.
You may not be able to eliminate the fear completely, but you can learn to overcome it.