Blizzard is primarily is PC game developer, and where PC games are, PC demos usually follow. Well, ever since Blizzard got its feet wet with the GBA, they figured that a GBA demo wouldn't be such a bad idea, either.
There is now a Shockwave demo version of the recently released Rock N' Roll Racing, complete with the classic opening music. It'll let you play one track a few times, complete with weapon and vehicle upgrades. Those interested in the game would do well to check it out.
You can find the RnR demo here, and Blizzard's other GBA demos over yonder. Remember, you need Macromedia Shockwave in order to play.
