Change your Default Alert Sound

An introduction to the Sound pane, change the sound effects your computer uses, as well as your input and output devices

How to Open the System Preferences in Mac OS X Leopard

Change which device is used as your input device (a microphone)

Choose which device is used as your output device (your speakers or headphones)

Disable computer sound effects (ex: when you empty the trash or change the volume) and Front Row effects