I'd turn my speakers off.
Nice try, but installing Vista creates an electromagnetic field around your speakers, and if you try to turn them off, you get zapped. If your speakers are not turned on when installing Vista, then Vista will turn them on for you, like it or not. :O)
On some laptops, there isn't really an independent "off" switch for the speakers. Instead, there's a switch that sets the Windows sound setting to "mute" -- a setting that would be overridden for the Vista startup sound, if Microsoft persists in this plan.