Birth plans are most useful when you educate, inform and reinforce the birth plan with good choices. If you want a normal, natural birth, stats say your worst choices are private Ob, private hospital. Find a doula (50% less c/s, 30% less forceps, vaccum etc) and get some good birth education. The Pink Kit, the Thinking Woman's Guide to a Better Birth, Ina Mays Guide to Childbirth... anything on the BB recommended reading list.
At the risk of being repetitive... Absolutely agree.

It's great to do a birthplan but it's really important to make choices that are going to give you the best possible chance of seeing it come to fruition. And that all starts with education.

Unfortunately there is not alot of really useful or empowering information being given to pregnant mums via the mainstream health system so you really need to take responsibility for educating yourself. Do some reading (have a look at the store here, or do a search on natural birth at Amazon, or Capers) - some good authors to start with are Sarah Buckley, Sheila Kitzinger, Janet Balaskas, Ina May Gaskin, Henci Goer, or Michel Odent. The Pink Kit that Kelly mentioned is also a fantastic resource for both mums and partners.

Independent birth classes are also a good place to start. Do a search for active birth classes in your area, or have a look at some offered by the Childbirth Ed Assoc (CEA).

Once you have those things in place, you'll be in a really good position to do an effective birth plan - because you'll know your stuff, you'll know your options and you'll feel confident in your choices....which gives you a much better chance of being able to follow through with them.

Congratulations and all the best