Icon Tweaker is a light and freeware application that helps you to customize and change the default icons of Windows.Icons are one of the main part of any OS looks and feels and can determine the coolness of your desktop
.Although the icons included in Vista are quite cool but the XP’s icons are old and not so cool.
So this tool will help you to change many icons of your windows.Being a freeware tool it has grown very popular and many icon sets are available for it.
Here’s a screenshot of its interface :-

To change a particular icon you need to select it click on change,browse through your favourite icon and then apply the changes.You can also restore the default icons if you wish in future by clicking the restore icon button.
For icon designers like me, Icon tweaker provides to develop Icon sets for it.Icon Tweaker now growing continously to become very popular provides a great platform to developers as the Icon Tweaker’s Icon Sets are downloaded at a high rate whether it be on Deviantart or on Customize.org .
To create a new theme click on the theme editor tab and start putting in the icon.Remember to Archive your icons by using the “Theme Archive Builder” .

You can download Icon Tweaker From
here!
Offical site
here !
Have a Nice Day And Enjoy!