Apparently, Real Networks will offer the service as an extension of Listen.com's Rhapsody, which Real Networks owns. Currently, Rhapsody boasts a library of 25,000 albums, which should give users access to at least as many tracks as Apple's iTunes Music Store, whose library consists of 200,000 songs.
Until Apple releases a Windows compatible version of iTunes, there's certainly plenty of room for Real Networks to carve a slice of the pie. If Real Networks is able to offer audio quality, music selection, and burning freedom that's comparable to what Apple offers with its iTunes Music Store, Apple could even lose a few budget-conscious consumers looking to save 20%. iTunes is widely regarded as one of the best media players available, but playback software may matter little to those who will just burn tracks to CD anyway.