Kim,
I used to be nervous of singing / playing in front of anybody, I have seen a lot of singers and musicians, and though I am in no way the worlds greatest, I am not the worst either, playing and singing with people who have a greater ability than yourself is daunting, but is also very beneficial, most people are only too happy to encourage and compliment, they have all been there and know how you are feeling, and I know a lot of big names who still get nervous, even though you wouldn't know it to look at them, remember you haven't got a reputation that preceeds you!
I found this poem in a book in a pub once, its so true...........

Whatever you are be that
Whatever you speak say true
Straightforwardly act,
Be honest, infact
Be nobody else but you.

Good luck, it'll be a breeze once you relax into it!
Let us know how you get on!
Lucy