I like Wesley's advice.

I always found it much easier to play or sing in a group than as solo. There was just something about the feeling of supporting someone else's playing and the dynamics of making music with others that eliminated the jitters for me. A solo performance was quite different though.

I did have to present lectures to crowds of 200-400, and I discovered a very important guideline. If you are speaking to ~150, there is an intimate feeling of communicating with individuals. But over 150, you lose that feeling, and you might as well be on TV. The most important thing I learned was, in presenting chemistry lectures which involved lots of explanations of problems...if you make a mistake with an audience of 150, you can correct it and go on. If, however, you make a mistake in front of a larger audience, it's almost impossible to correct it.

For you this means, be over prepared! Check out the logistics of sound and light beforehand, and have back up plans. Have multiple starting places. Don't be shocked at the lack of intimacy. Plant friends in the audience to assist the "spontaneous" applause. Keep moving. Also, be prepared for the noise level. You might even have to alter your choice of songs. I really don't think jitters will be as big a problem as presentation.

Let us know how it goes.

Mary