Evil Steve at GameDev said this about the DirectSound and hardware acceleration:
"If you're using notifications to signal that you're reaching the end of the buffer, they're very very broken on a lot of hardware (Especially on-board audio controllers). The solution is to use software buffers for streaming. On Vista, DirectSound isn't hardware accelerated at all, so the buffers will be forced into software even if you specify hardware - which means the notifications will work correctly."
I just test using software buffers for streaming and it works.
