Can you use the XNA framework to write games for XBox Live Arcade that require Rock Band or Guitar Hero instruments?
According to this site (http://blogs.msdn.com/b/dawate/archive/2008/02/05/building-a-3d-game-in-xna-from-scratch-free-video-tutorial-series-now-available.aspx), the Guitar Hero buttons map directly to the standard control on an Xbox 360 controller. Here's what it says (has a video and everything):
10). Determining What's What On The Guitar Controller The controller for Guitar Hero games maps directly to controls on a standard Xbox 360 controller, but It's not immediately obvious what exactly the whammy bar, strum bar, and orange button do. Rather than go hunt for documentation, we can find out by experimentation in less than 5 minutes.
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I haven't watched it, but I have seen other games that used a Guitar Hero controller in XNA. Good luck!
The XNA documentation includes an article that lists how various alternate 360 controllers map to the gamepad buttons and triggers: Using Alternative Input Devices (Xbox 360).
Also, despite the article title, the information applies to PC as well, since those alternate controllers will still appear as the gamepad under XInput on Windows (and therefore to XNA).
The short answer is yes-ish. The controllers for the most part just send standard button inputs which is why they can be used in the dashboard. More recent stuff like the Pro Guitar for Rockband3 probably aren't accessible with XNA, but the standard controllers sure.
You should be able to use this older utility to see what maps to what on the controller