5
It was working up 3rd Sept, and on 4th Sept I see an optional update for Intel Graphic Chipset from Microsoft. I am not sure but it stopped working when I tried to do voice chat on 5th Sept.
If it worked before the update but seems to have stopped after it, them maybe using system restore to bring your computer back to a time prior to the update would be my first check. If that cures it, it's the updated.

Did you update to Vista or did the computer with vista pre-installed?