I've had a lot of fun with sounds.. Here's how:
To find sounds on web: go to Google and type in sounds (you can be as specific as you like eg birds, thunder etc. Open a new folder on any drive you want and collect them in there.
To assign a sound to a puter function (with Windows) click Start, Settings, Control panel, then dbl-click Sounds. A dialog thing opens showing all the different functions and a Browse button to select the sound you want from your collection.