you know you can view windows 7 themes before downloading them from the Personalization Gallery via Bing Visual Search, although Visual Search is available and accessible in full versions of Bing, you can switch to United States-English .
Just select a theme and click on it, the theme details will be shown like how many wallpapers included in the theme pack, preview these wallpapers shown as thumbnails in the Zoom In frame, a short description about the theme. Click on a specific image to view the slideshow of all images in the theme.
If you are not satisfied with a specific theme, you can select another one and preview it and download the theme to your computer.