beg/rent/'steal'/borrow spare batteries for your D80, a flash or two and make it at least SB800, spare memory cards, spare camera body, spare flash batteries, light modifier like flip-it/bounce card/lightsphere/whale tail/sharks fins (er...just kidding).
Are you going to be the only photographer? Are you being paid? What does your friend expect you to capture and deliver? Is he expecting pro-grade photography? These are important things to clear up with your friend.
It is also good to let your friend know that you are relatively new to photography and to not expect too much from you, or demand too much from you. If your friend is gonna depend on you to capture all the vital moments, make it clear to your friend about your capabilities, what you can and cannot achieve, and that if he wants all the memories captured safe and well, to hire a pro.
No offence to you, but weddings are one-offs and cannot be redone if the moment is missed.
thanks. Will let him know that I'm really new into this. But I think he is having a big time budget issue hence I'm there to help him cut cost. I think I will get a SB600 or SB800. Thanks for all your help though!