Joe Shervell of London Speaker Bureau suggests your fear of speaking may be due to thinking about the situation (e.g., thinking "This speech has to be interesting"). If this is the case, analyze what is making your nervous and make your thoughts into speech goals (e.g., What would I have to do to make my speech more interesting to my audience?).
Tim Wilson
Professional Speech Coach
Free speaking tips at: http://speakingquicktips.blogspot.com