RealNetworks' Harmony software will allow songs from its own store to work on Apple's iPod and iPod mini. A pre-release version of Harmony will be available for download this week.
The method seems like a kludge however. The Harmony software keeps track of what audio player the user has, and then converts the native song format to the appropriate format for the player. RealNetworks already uses AAC, so that isn't an issue for the iPod, but the songs have their own form of copy protection that the iPod does not understand. It seems that if the Harmony software detects an iPod, it will change the copy protection to a reverse engineered version of Apple's FairPlay, which the iPod can read.
RealNetworks use higher bitrate AAC files than Apple does, and thus RealNetworks does have an advantage over Apple in this regard. However, iTunes is rated to be the superior software.
Since Apple has not licenced FairPlay to RealNetworks, expect to see some strong legal statements from Apple in the very near future. Earlier this year, RealNetworks had offered to pay for FairPlay licencing, but Apple refused.