When installing Windows 7 onto a computer, it prompts you to select your language and location.  Based on your answers, it will automatically select the Aero theme which best meets your region.  Since I am located in the United States, by default I am only able to choose themes from the United States.  This article will show you how to access the other themes already located on your computer.

1. Select start, type in C:WindowsGlobalizationMCT
2. A window will open showing you a MCT folder for Canada, Australia, South Africa, and Great Britain
3. Open a folder for a respective country, this example I will use Great Britain : C:WindowsGlobalizationMCTMCT-GB
4. Open the theme folder located under that country: C:WindowsGlobalizationMCTMCT-GBTheme
5. Double click on the GB file
6. Now your theme has changed to the Great Britain  theme
7. If you go to personalize your desktop, the Great Britain  theme will now be permanently seen there
8. Repeat the steps above for each countries theme.