I've been all over the Acer site but I'd be guessing trying to figure out what driver actually enables those keys and if it was compatible with my 5920. I even put an audio CD in the optical drive to see if they were tied to the drive and they still didn't work. Vista was short lived on it so I don't know if they even worked before I installed windows 7. I'm just hoping to get lucky if someone else ran into a similar deal and solved it. The manual lists them as Media buttons, for use with Acer Arcade and other media playing programs. I installed Acer Arcade but they didn't work with it either? I don't know maybe they are broken.
The Acer Hd audio manager doesn't list anything to do with hot keys, just jack assignments etc.