Windows 7 Themes and wallpapers are amazing as compared to Windows vista. Microsoft windows 7 has default 5 theme but Windows 7 beta 1 build 7000 onwards has several hidden & locked themes provided for regional countries such as Australia, Canada, Great Britain, United States and South Africa.Since these hidden themes are installed along with your Windows 7 installation you can unlock/unhide these hidden Windows 7 Themes for regional countries.
Here's How To: Unlock Hidden Regional Themes In Windows 7