Agree with @boazjoe. I've created several tri-fold brochures using the pages templates. They come out looking really nice. Highly recommended. If you don't have Pages, it's only $20 at the MAS.
not exactly the answer to your question, but this has proved to be a most useful freebie for me to create booklets simply and irrespective of how many pages one's using (obviously in multiples of 4)