The header file - Wpdmtpextensions.h - has been referenced in several of my posts and is needed to talk MTP to the device through WPD. The header file is not available in the Vista SDK/WDK or the WMP 11 SDK, but is planned for inclusion in the Windows Server code name "Longhorn" SDK.
I've just received a heads-up from the WPD team that the Server SDK has been published as a Beta (link). Once you install the Server SDK, you can copy over wpdmtpextensions.h file to your desired SDK (e.g. Vista SDK/Visual Studio SDK) include folder if needed.