First, know that the fact that you are having some nervous feelings is completely natural and shows that you understand the enormous undertaking and sacred journey you are about to embark on....
Your body was built for birth. What is amazing is that our bodies take the amount of pain we experience and create endorphins to help us cope. Women that have natural births often zone out and sleep between contractions - some worry that women are too exhausted to continue. While lack of sleep is one part of it, the greatest part are those endorphins kicking in - allowing her to ground herself and focus inward, resting for the next contraction.
Labor is painful for many women. However, unlike horrible menstrual cramps, or getting your arm sawed off, the pain of contractions come and go. Savor the breaks. In a 90 second contraction, the worst pain is about 45 seconds. Your body is working WITH you during this time - not against you. You are merely along for the ride. Trust the whole process.
Create your birth environment. If you're birthing in the hospital, there's nothing wrong with taping a sign on the door saying "quiet voices and dim lights appreciated". Every person that walks into your birth space will impact your energy. This sign - or the presence of someone to remind them - will ensure that your space is peaceful and intimate - the perfect atmosphere for letting go and birthing your baby.
(White Christmas lights are a nice way to have a soft glow away from fluorescents when you cannot have candles around - just a bunch of lights plugged in, atop a counter or shelf makes such a difference!)
When you will be giving birth, you can focus on the hundreds of thousands of women who will be birthing at the same time - most of them unmedicated. Use their strength. You're all in it together.
Use water when you can. Showers, baths, hot packs on your back or lower belly are wonderful.
You have all the tools you need to birth naturally. You could do it alone, with nobody around. Remember this. If somebody in your space is wrought with fear or anxiety, ask them to leave. Do not be shy about what you need in birth. It's YOUR experience. When you feel safe, you birth smoothly.
You have a deep cellular knowledge about birth right now. It has been handed down to you from the line of women who birthed before you. It's ok to ask (through prayer, meditation, etc.) for their assistance and guidance.
You CAN do this. Your body is perfectly designed to birth this way. Your baby is so wise - and works intuitively with your body.
I don't know if this has helped at all - but I know that the other wise, wonderful women here can offer some more suggestions and inspiration.