I went on my Uni's presentation skills course - it was helpful, if only to realise that everybody is scared!! I find that I am less nervous if I know that I have prepared well (lots of rehearsals, if only to yourself). Helps to have a back-up plan in case of technical difficulties e.g. take along some OHP acetates as well as your Powerpoint presentation, just in case of a software compatibility problem. If possible, test out the presentation in the place where you will have to deliver it before the big day. Good luck! :o)