Hi Mozart,
did you read this ->
There's a project called yaamidrum similar to yours hosted on sourceforge:
To give an answer to your question->
Maybe this helps:
- http://hunt.net.nz/users/darran/weblog/5b7f8/
- ttymidi (for linux users)
- http://www.instructables.com/id/Turn-your-Arduino-Uno-into-an-USB-HID-Mididevice/
Have fun!