In short, Rock Band Network is a service that allows just about anyone to turn one of their own garden variety songs into the kind of song you can click colored buttons along to in Rock Band. Tracks can then be shared and even sold to other users, with the track creator dictating the price. The creation tools at hand are a tad more complex and intricate than the midi-tastic ‘Music Studio’ mode offered by Guitar Hero, but the end result is comparable to the kind of quality you’d expect from a regular Rock Band release.
Some are keen to capitalize on the apparent complexity, with companies such as TuneCore. Inc offering to transmogrify your track into a Rock Band-friendly track for an ample fee (by ‘ample’ I mean $999 as an introductory rate).
To get involved, head over the official Rock Band website to sign up for the Rock Band Network beta, which is currently only available to Xbox 360 users.