IconTweaker is a freeware application that allows you to customize all your Windows icons. Icons are one of main parts of the Windows interface. Customizing them can make your desktop look better and can also improve the usability, because you can make it easier to recognize items.
Using the IconTweaker theme system, designers can share their icons with other people. IconTweaker has an open XML-based theme format that can be extended using plug-ins. If you created an IconTweaker theme for your icons, you can be sure they can be used by everyone. Many themes with beautiful icons are already included and ready to use.
(source: http://en.softonic.com/)