http://blogs.msdn.com/windowsmobile/archive/2009/06/04/sdk-dtk-drk-wtf.aspx
SDK: Software Development Kit
We have not released a new SDK for Windows Mobile 6.5. The Windows Mobile 6 Professional SDK or Windows Mobile 6 Standard SDK are required for Windows Mobile 6.5 application development.
6.5 依然沿用了Windows Mobile 6 的SDK。
听说wm6.5的sdk微软曾经发布过，后来又匆匆撤（说是不稳定）。在网上搜索了半天也搜索不到wm6.5 的sdk，搜到的大都是wm6.5 DTK(主要就是有个模拟器)。
DTK: Developer Toolkit
The Windows Mobile 6.5 Developer Toolkit (DTK) is not an SDK! The
DTK contains emulators, gesture APIs, and samples useful for developing Windows
Mobile 6.5 applications. You will still need to install Visual Studio and the
Windows Mobile 6 SDK prior to running the toolkit installer.
DRK: Developer Resource Kit
The Windows Mobile Developer Resource Kit (DRK) is an offline DVD copy of the
most useful and relevant Windows Mobile application development tools and
resources. Traditionally the DRK does not contain any exclusive content, in that
nearly everything on the DRK is available for download online. This time we are
pleased to publish the Windows Mobile 6.5 DRK with several sample chapters of
Microsoft Mobile Development Handbook from Microsoft Press (Wigley, Moth, and Foot).
We hand out free copies of the DRK at several conferences and developer
events throughout the year.
WTF: Where To Follow?
Follow us on Twitter @wmdev to get the inside scoop and up to date information for
development on Windows Mobile!
Lastly, you can find the latest development resources at http://developer.windowsmobile.com/.
*UPDATE* Documentation has been released for Using
Gestures in Windows Mobile 6.5. Thanks for your patience!