System (BIOS) Beep

So there are the Windows sounds in Windows.  They can get annoying, but you can usually affect the volume with the Windows volume settings to make it better.  Vista helps a lot here by providing a "source" mixer.

There are some beeps, however, that are not Windows sounds.  This beep may happen to you, for example, if you hit more than 2 or 3 keys at the same time.  Here's how you can disable it:
(From: http://www.howtogeek.com/howto/windows/turn-off-the-annoying-windows-xp-system-beeps/)

Disable Beep in Device Manager

Open up Device Manager by right-clicking on Computer and choosing Properties, then on the Hardware tab you’ll find the button for Device Manager.

Select View \ Show hidden devices from the menu.

Find Non-Plug and Play Drivers in the list, and then right-click on “Beep” and disable it:

When it prompts you to reboot, select no, and then right-click again and choose Properties this time. On the Driver tab, change the Startup type to “Disabled” and then click the “Stop” button if you are able to.

This should disable the system beep speaker, but it probably won’t change the volume control beep, so continue on.