Modding Mac OS X by Erica Sadun an O'Reilly Publishing
http://www.amazon.com/exec/obidos/ASIN/0596007094/macintoucwebsite/ref%3Dnosim/002-6881264-1054415
$16.97

Quote:
One of the reasons for the Macintosh's popularity is that it empowers Mac users. Mac users can and frequently do customize and control their applications, creating just exactly the user interface they need or envision. With Mac OS X, Mac users have more power and possibilities than ever before, but some of those possibilities are hidden a little deeper in Mac OS X. Modding Mac OS X: Extreme Makeovers for Your Mac uncovers dozens of ways to hack the user interface for both Mac OS X and the applications that run upon it, using the newest tools; from hacking the preferences, enabling and disabling plug-ins, to using the Terminal and applications like the Property List Editor to tweak files and edit resources, and much more. If you want to take Mac OS X further, to tweak and experiment, to create and refine, to customize and control and have some fun doing it--Modding Mac OS X is an indispensable guide.