Some of you may be knowing this and some of you may not, but yes Windows 7 has some predefined hidden themes that can be used.
These themes come along with Windows 7 but are hidden inside the Windows folder.
How to access these?
Browse to C: (Basically the folder where Windows is installed) and then go to Windows folder and open Globalization.
Here you will see two folders : ELS and SORTING
Now in the navigation bar above click once and type in the following code:
C:\Windows\Globalization\MCT\
Now you will get five folders (starting with MCT-…) which will have different themes in it.
You can install and apply these themes.