Stop! Don't buy another audio CD until you have read the rest of this column. Windows software is making big changes in the way we buy, store, and play back music in our offices and homes.

The force behind this change is a music compression standard known as MP3. With the growth of the Internet, musicians around the world who don't have a contract with a recording label are converting their best tunes to the digital MP3 format and distributing them free as a method of promotion.

Thousands of such songs are now available on the Web. Anyone can play these selections on any multimedia computer equipped with speakers and software, such as the Microsoft Media Player that comes with Windows 98.

This underground music movement might have remained unknown to most consumers if it weren't for a lawsuit filed by the Recording Industry Association of America (RIAA). The suit, filed against Diamond Multimedia, was an attempt to stop Diamond from distributing a $US200 pager-size MP3 player called Rio. Using a parallel port adapter (with a pass-through for a printer), you download MP3 files from a PC into Rio's memory. The device plays an hour or two of music through headphones or speakers. It's the ultimate in portable music enjoyment.

As I write this, the RIAA suit had been denied in a federal court in California. The RIAA has appealed, but it appears that MP3 music is an unstoppable force that will shape our listening habits for years to come. Even if the RIAA suit is successful, Diamond would have to pay only a 2 per cent royalty on all Rio devices and add anticopying circuitry to discourage piracy of copyrighted songs. Two per cent seems to be a small increment that wouldn't significantly harm Rio's market.

Special Windows software bundled with Rio units is a major factor in MP3's popularity. MusicMatch Jukebox, a US$30 shareware program, enables users to convert tracks from any audio CD into the MP3 format. Once you've converted your audio CD collection, you can use Jukebox to play songs in any specified order (or random order) on your multimedia PC. Or you can download the songs you want to your Rio and go anywhere with them.

I recently interviewed the owners of MusicMatch, husband and wife Dennis Mudd and Pamela Evans. They see an explosion of new music that multimedia PCs have made available. Their Web site, www.musicmatch.com, is a haven for international musicians who have contributed one or more songs in exchange for the ability to sell their home-grown CDs through MusicMatch.

The "fair use" provisions of copyright law allow any buyer of copyrighted music or other media to make a copy for his or her own personal use. For example, you can copy a chapter of a book to read on the bus. But what about sharing songs with others who aren't buyers of the original CD? Many of the songs found on "pirate" Web sites are pure copyright violations.

Mudd and Evans say pirate sites are quickly shut down by music-industry lawyers ù and in any event there's plenty of good music to choose from that bands want you to share.

Soon, all music, books, movies, and TV shows will be distributed this way ù so we might as well get good at it.

Brian Livingston's latest book is Windows 98 Secrets (IDG Books)