That's not right. The series was originally written in this order:
1 - The Lion, the Witch, and the Wardrobe
2 - Prince Caspian
3 - The Voyage of the Dawn Treader
4 - The Silver Chair
5 - The Horse and His Boy
6 - The Magician's Nephew
7 - The Last Battle
The Magician's Nephew was conceived by Lewis only after the success of the earlier books, to respond in a way to fans, to explain how Narnia was created. It wasn't first. Only recent publications of the series have printed it in this different order. This chronological order goes 6, 1, 5, 2, 3, 4, 7. I have read the series in both ways, but The Lion, the Witch and the Wardrobe has always been "first" in my mind. It is the most fitting introduction of Narnia, and reading 6 before 1 will spoil some of the magic of 1, such as learning who the professor really is.
That said, I love these books. I saw the animated movie of the first book years ago, but that's not where the real magic is at. In the late 80s, the BBC made a TV series out of the first four books, and edited them into three movies.
The Lion, The Witch, and the Wardrobe
Prince Caspian and the Voyage of the Dawn Treader
The Silver Chair
They are out on DVD, and are well worth it for the Narnia fan. The White Witch overacts horribly, production values are low, and special effects are pretty bad, but still, there's something about the gritty tone of these movies that really work for it, especially in the darker parts of The Silver Chair, and the last parts of The Voyage of the Dawn Treader (Caspian and Dawn Treader have been combined into one full-length feature). It really is too bad that they didn't get to make the last three. Hopefully these new movies will be a success and we'll get to see all seven fully realized.