to unlock the hidden windows 7 themes just follow the steps
1.open up explore on the bottom icons
2.at the top click on organized, and click the folder and option
3.click the view tab and under the view tab select the show hidden files folders and drives (click apply and click okay)
4.go to the path bar at the upper side delete the words libraries and put \Windows\Globalization\MCT\
5 in there you gonna find 5 folders containing 5 themes of different country click each theme folder and double click themes and it will be automatically add into your themes..
hope it help...