Volume Control in Vista

hi,
i have few questions regarding volume control in vista.
as far i know WASPI, ie Windows Audio Session can be used for volume control
and for multimedia, but when i search for WASAPI i'm unable to find it in
online MSDN,
and i found some sample code which is using "mmdeviceapi.h" and
"audioclient.h". but this header files are not available on Windows SDK
(directory in Windows Vista)

and then i found this :
http://www.freelists.org/archives/wd.../msg00046.html

which says :
The headers for these new APIs may not yet be available, but they will be
available in a Vista SDK update soon(ish)

so when will we get this header files available.