M.J.
I am a mother of 4 and have nursed all my kids till they weaned themselves at about 18 months of age. Going at least one year is best so you never have to give them formula. Also, I started my kids on cups at 5 months of age so I would never have to deal with taking a bottle from them. Just do what feels right to you. I have many frineds who nursed till there child was 2-3 years of age. Breastmilk is best for baby for several reasons. Go to your local library and check out the La Leche League Book, it is a great resource. Also remember that you are going to get lots of unsolicated advice from family and friends just take it with a grain of salt. Mommy knows best for YOUR child even when your a first time mom. You Rock Mommy!
Best of Mothering,
Mother of 4, M.