Rachel Greenham has written a very good tutorial called 'Subversion for Writers.' If you aren't a coder, you probably aren't familiar with the popular version control system, Subversion. It allows you to work collaboratively with folks on the same files (in most cases code) without fear of overwriting the work of others. Subversion tracks all the changes made to those files, and who did them, and allows you to rollback changes or branch off into different directions with having to worry about mucking up the entire project.
Rachel, being a geeky writer, immediately saw the potential of using Subversion for writers. Her tutorial walks you through what Subversion is, how to install it on your Mac (if you're running Leopard it is already installed), some apps you can use to make interacting with Subversion easier, and how to track your changes. To be clear, this method is not for everyone. If you aren't comfortable with the Terminal you should steer clear of this, and if you don't revise the same document over and over again you'll have no need for it. That being said, it is a very clever idea.
[via the Hog Bay Software Forums]