How to revert OS X Snow Leopard default theme?
Aqua Extreme comes with a separate package called Remove Aqua Extreme which restores the default user interface.  

If you download the latest Aqua Extreme from http://www.maxthemes.com/downloads/Aqua%20Extreme.dmg
you will find the Remove Aqua Extreme package inside the installation bundle.

Run this package, it should restore everything.