"Microsoft is making a tech-demo version of its upcoming DirectX 10.1 available via download, including a version of XAudio2, the company's cross-platform replacement for DirectSound."
"Users can try out both via the 468-Mbyte version of the August 2007 DirectX SDK. There's a catch, though: the August 2007 Direct3D 10.1 Tech Preview requires the Windows Vista SP1 Beta which will be available to MSDN subscribers once it is publicly released, according to Microsoft.
According to Microsoft, "Direct3D 10.1 is an incremental, side-by-side update to Direct3D 10.0 that provides a series of new rendering features that will be available in an upcoming generation of graphics hardware." The XAudio2 technology is also used in the Xbox 360, and will eventually replace DirectSound as the PC's main audio driver, according to Microsoft."
Softpedia: Microsoft: DirectX 10 Hardware WILL Support DirectX 10.1