As announced, today Microsoft released the Windows Phone 8 SDK!
It consists of a full-featured development environment to use for building apps and games for Windows Phone 8.0 and Windows Phone 7.5. The Windows Phone SDK provides a stand-alone Visual Studio Express 2012 Edition for Windows Phone or works as an add-in to Visual Studio 2012 Professional, Premium or Ultimate.
With the SDK, it is possible to use levearage existing programming skills and code to build managed or native code apps. In addition, the SDK includes multiple emulators and additional tools for profiling and testing your Windows Phone app under real-world conditions.
To run the emulator Windows 8 Pro x64 edition and a processor that supports Second Level Address Translation (SLAT) are required. If a computer does not meet the requirements for the Windows Phone 8 Emulator, the SDK will install and run, however the Windows Phone 8 Emulator will not work and developers won't be able to deploy or test apps on the Emulator.