How can I write a book on my Mac witout buying special software. or do I need special software>?

Open Office is cool, but try Neo Office. It's free and is OS X native and doesn't need X11 installed. I'd send them a donation if you like it since it helps create more and better open source stuff like that.

http://www.neooffice.org/neojava/en/index.php

Anything from Microsoft is like so way overpriced as to be insane so with this you bypass that.

Any word processing software will do. I would get Word (in case you don't have it) because that is what most people have and when you get ready to send it out, you won't have to worry about an agent or publishing company not being able to read it.

OpenOffice for Mac comes with a powerful word processor. It's free.

Go to http://www.openoffice.org/

I don't have a Mac, but what sort of word processing program do you have? That's all you need! On my PC, I have Word ... WordPerfect ... WordPad ... and Notepad (listed in the order I would choose to use them). Hope this helps!

better to write a blog online. then when you are done with the book/ blog. you can just retrieve all data to your mac, to organize everything. you can use convert it to pdf, and use lulu.com to sell it.

do it online for free.