Would you mind if for now it only set the master volume to 0%?
I can do the rest, but not in next few days.
Just place this on the startup group on the start menu.
PS: I just noticed something important: You probably want this to hide the windows startup sound too, but that's impossible. The windows startup sound is "sounded" (that doesn't make much sense, does it?) before the startup programs are launched. Thus, when this program starts, it'll be too late.
PS2: i think i know how to solve it. The sound volume could be set at shutdown. For that, you'd need to have an app always running that would only serve this purpose.