Windows Phone SDK update adds Windows Phone 7.8 Emulator and features
Available today, the Windows Phone SDK Update for Windows Phone 7.8 is an optional update that adds two new Windows Phone 7.8 emulator images to your existing SDK installation. These two emulator images should enable you to fully test how your Windows Phone 7.5 app’s Live Tiles will look and behave when they are run on a device running Windows Phone 7.8.
The SDK update requires an existing installation of the Windows Phone SDK:
If you have both the Windows Phone SDK 8.0 and Windows Phone SDK 7.1 installed on the same computer, both SDKs will be updated.
If you have a Windows Phone 7.5 app in the Marketplace, it is highly recommend downloading the Windows Phone SDK Update for Windows Phone 7.8 today and starting to experiment by using the new tile options in your app.