To better support the multi-monitor setup, Windows 8 themes have features that are not supported in Windows 7. Therefore, you cannot open Windows 8 themes on a Windows 7 computer, at least not directly. It sucks because those only Windows 8 and Windows RT supported themes on Microsoft Personalization Gallery look awesome.
Thanks to Into Windows, there is a workaround that allows us to port a Windows 8 theme to Windows 7 system, though those Windows-8-only features will not be available.
Basically, here is what you need to do.
1. Download and extract the content from .deskthemepack file. 7Zip is your best friend to easily achieve this.
2. Go to Desktop Background in Desktop Personalization window.
3. Click Browse… button and select the desktopbackground folder you extracted earlier.
4. Click OK, and Save changes. You will notice the desktop background is changed immediately.
You can save the theme and share it with others by right-clicking the unsaved theme and choosing Save theme for sharing.
Not difficult, isn’t it? It’s worth spending a minute or 2 to do so if you really like the desktop wallpapers from a windows 8 theme.