Microsoft is set to enter the online music fray tomorrow with the launch of a test version of its MSN Music store and release of Windows Media Player 10.

The software maker shall also provide more details about the availability of Portable Media Centers, devices that run a slimmed-down version of Windows and can play back audio and video. The first Portable Media Center from Creative Technology should be available this week.

While Portable Media Centers will compete with Apple's iPod on some fronts, industry watchers consider the Microsoft-based devices a new category of media players. Portable Media Centers are much larger than iPods and also play back video, while iPods only play audio.

The MSN Music store is expected to offer songs from all major music companies and to be accessible from within the Windows Media Player as well as through a web browser. The store will compete against Apple's iTunes and other online music services such as RealNetworks's RealPlayer Music Store and Rhapsody service.

RealNetworks has lowered prices in its download store as part of a special promotion ahead of Microsoft's launch. The company has also announced it recently sold over 1m songs in a week, the highest number of songs sold in a week in its store.

Microsoft has been working on its music download service since last year. Company executives have said that the store won't be a money-making service, but rather is something the company has to offer to for its range of services to be complete.