Apple has released iTunes 7.2 which is available through Software Update. It includes the new iTunes Plus feature which allows you to purchase, and upgrade music to a DRM-Free style with higher quality.
Although, at this moment the iTunes store does not have a lot of DRM-Free content available. Steve Jobs made the announcement of more DRM-Free tracks being available in the store at the “D: All Things Digital” conference the other day, possibly up to half the music in there will be DRM-Free eventually, hopefully all someday. The new DRM-free tracks will cost $1.29 compared to the locked DRM tracks at $0.99, but give you that DRM-Free goodness as well as a bit more quality over the $0.99 tracks.
If you’ve already purchased a track for $0.99 and the DRM-Free version is available, there is no need to re-purchase the song. With iTunes Plus you can easily update your tracks to DRM-Free tracks for only $0.30.