Well arduino already works with MAX/Jitter 
You just need to use the serial port patch and send a stream of bytes to it.
I had an arduino board read an analogue joystick and send data to a Max/Jitter program as part of an exhibition that was running for 2 Months at the V&A museum in London.
The MAX code was written by the designer of the piece (Michal Rinott) therefore I don't have a code sample to post
I'll try to find an example to publish
massimo