How to set the master volume

Hello,
I would like to set the PDA master volume.
I tried to use FMOD library to do this but it doesn't work.
Anybody knows how to do ?
Thanx

The FMOD library is for the musics and not for the master volume
For the volume I thing there's a DWORD value in the registry in Microsoft\State but I don't know where... After that you've to refresh the sound statut...
Else I thing there's an other solution...