As a former horribly shy person, I used to have the same problems with speaking in front of a group (even of one!). I took speech in high school, but it just made me a wreck. Finally I ended up teaching Yoga and had to talk every day (I had eight classes per week!) to a group. I pulled it off because: 1)I loved the subject, 2) I knew the material cold, 3) I was really motivated to share what I knew, and 4) my audience was interested in the subject.

After that experience I ended up teaching martial arts for several years, and eventually became a licensed Instructor/Coordinator in Emergency Medical Services Technician training. It helped me in my work as a Systems Analyst where I often had to explain technical aspects of computer systems, and generally made me an extrovert.

I think the information presented before is really, really good. The most important thing, I think is to know your subject, and have enthusiasm for it. This will be communicated to your audience, and they will respond. After that you will be on a roll. The problem is when you are not sure of your expertise and the audience senses this. Speaking in public will give you immense feed-back, positive or negative, depending on how you start your speech. What ever you do, DON't try to fake something you aren't sure of. Admit you don't know, and go on. You will be seen as an honest person, and this will add to your credibility.

Good luck, it comes with practice. As my mother used to say, "Dread doing it is the worst!"