Check out this amazing mod for Guitar Hero on the Nintendo DS, made by modder Eric Ruckman.
This cool Guitar Hero Controller uses a wireless PS2 Guitar Hero Controller, and cut out all the insides, as you can see from the photo the DS fits neatly inside the PS2 Guitar.
Here’s a video of it in action.
The controller buttons are connected to the DS by wiring tinto the adapter and Eric has also added a wireless FM transmitter so he can play it through his home sound system.