[PD] Arduino + Standard Firmata + Arduino MIDI interface

[Ingo]

Hi, I was wondering if I could use an Arduino as a MIDI interface while
running the standard firmata.

Does anybody do this?

Can the additional software simply be added to the firmata or is it
necessary to edit the firmata for doing this.

Does the Arduino need extra parts like opto-couplers?
Or is that stuff already on the board?
(I'm using a Duemilanove with Ubuntu)

I would appreciate if anybody could point me in a direction where I could
find some working MIDI software that can be added to the firmata.

Thanks!
Ingo