Specifics
Read this first

Mac OS X themes are small files installed on top of your graphic user interface (GUI) via a software called Shapeshifter. Once applied, the themes will change the entire appearance of your operating system (Mac OS X) making the look of your Mac unique. The themes were made primarily for Panther (OS X 10.3) and some have been updated to Tiger (OS X10.4).
While the studio still offers them for download, I decided (for various reasons) to stop their development and support. So, you can still use them but I won’t update or fix any bug you might find. Before downloading them, please read the disclaimer and the install instructions found below.

Posted on 12-18-2006
Disclaimer

All the themes have been thoroughly tested and are fully compatible with ShapeShifter 2.0. However, xiapdesign can't be held responsible for any damage caused from using any of the files available on this site. Use at your own risk.

Install instructions

All my themes are in guiKit format. Meaning that you need the ShapeShifter software from Unsanity to install them. Once you get ShapeShifter, double click on the guiKit file and ShapeShifter will take care of everything from there. The guiKit file will be installed in a folder located in the following path:
User/"your home folder"/library/application support/ShapeShifter guiKits. To use ShapeShifter just follow the instructions (very simple) that come with the app. That's it ;-)