Windows Themes Installer is a freeware portable utility which allows you to install a theme, remove a theme and restore defaults easily in Windows 7 & Vista.
Windows does not allow you to install 3rd party themes. You have to patch some system files to be able to do so. After patching the files, you may have to restart the PC.
INSTALL A THEME AND CHANGE SYSTEM FILES:
1. Run the tool as Administrator.
2. Select the options which you want to install:
* Theme
* Explorer.exe
* OobeFldr.dll
* ExplorerFrame.dll
* Shell32.dll
3. Once you have selected the options, click on the "Browse" button and browse for the file of the desired option.
4. Now click on "Install Theme" button to install the theme and replace the system files.
Please keep in mind that it is always advisable to create a system restore point before making any type of modifications to your PC.

RESTORE DEFAULT SYSTEM FILES:
To restore the default system files click on the "Restore Default System Files" button.

REMOVE A THEME:
To remove a theme select the theme which you want to remove from the list and click on the "Remove Theme" button.

APPLY A THEME:
To apply a theme select the theme which you want to apply from the list and click on the "Apply Theme" button.

The license of this software is Freeware, you can free download and free use this shell extension software.