When you first start the Windows 7 installation the first thing you will do is select a language, time and currency format. This is where Windows determines what themes you’re presented with by default.
Being from the US I’m presented with location specific themes from the United States with desktop backgrounds such as scenery from Maine, Idaho, Oregon etc.
To access the other international themes copy and paste the following path into the search box and hit Enter.
In the MCT folder you will find additional themes for Canada, Australia, South Africa, and Great Britain.
You can go in and grab just the Wallpapers…
Or go into the Theme folder double click on the the thumbnail to add it.
Here you can see I added all of them and now they will be available under the My Themes section for when you want to change them around.
This is a neat little trick that will let you customize Windows 7 with hidden themes already available. Also if you want to get more themes head over to the Microsoft site.