Practice your presentation. Not once or twice, but over and over. When I was in law school, I was terrified of public speaking, but I joined Moot Court to get over my fear. I did my speech over and over in my apartment (you may want to practice from an outline, instead of a word for word document, otherwise you may sound rehearsed). I even practiced in the shower. I would also recommend practicing it in an empty classroom or conference room when no one is around, if you can find one. Do some relaxation, especially the night before and the morning of the speak. The obsessive practicing works, I promise you...after my first Moot Court argument, the Dean of our law school asked my partner and I to join the prestigious external competition team. And to think that I was just trying to get through the speech without passing out!!
Good luck!