A sound card is a wonderful gadget. It can provide hours of entertainment, but it's also useful for business and general communications. Specifically, a sound card will let you do many things:

Personalize your computer. If you're tired of the same old dings and beeps from your PC or Mac, you can record voice, music or sound effects and substitute them for system sounds. For example, when your machine starts up, instead of hearing the same, old one-note chord, why not have a friendly voice say, "I'm ready to go to work," or a warning for your kids, "Better do your homework," or a couple of seconds of a favorite song. You can usually change system sounds from the control panel of your operating system.

Add voice notations to letters, spreadsheets and e-mail. If you're running Windows, you can record a voice message as a wave file, store it as a file on your hard disk and embed it into virtually any other document. You can use this to store reminders to yourself or messages to other people. When they call up the file with the word processor spreadsheet, they'll see a little sound icon. By clicking on the icon, they'll play the recording. Just remember to include the sound file with your document if you're transferring it to another computer.

You can use the same technique to record your voice, encode it, attach it to an e-mail message and send it over the Internet. Most PC and Mac-based e-mail programs will decode the file, and the recipient can play it using basic media-player software.

Play a music CD while you work. Music CDs and computer CD-ROMs use the same method to store data. You can put a music disc in your CD-ROM drive and use Windows' Media Player to start it up and switch tracks. Your sound card or computer may have been packaged with more sophisticated software that turns your screen into the front of a stereo system. That means you can program the CD player.

Just don't expect miracles. Your sound board isn't as good as a real music amplifier, and your PC speakers can't match the output from your stereo system. But all things considered, computer sound isn't half bad.

Build a MIDI music library. If you're reading this text, you're on the Web. That means you have access to huge libraries of MIDI files. Musicians all over the world have translated popular and classical music into MIDI format and are happy to share their creations.

To use a MIDI file on the Web, just download it and open it with your MIDI software or media player. One of the neat things you can do if you have MIDI editing software is experiment with any score by changing the instruments around. Want to hear the William Tell Overture played on glockenspiels? You can do it.