There are some tutorials for interfacing Arduino with other software package in the playground wiki:
Arduino Playground - HomePage (look in the sidebar on the right):
Arduino with Flash: Arduino code&examples - by b of Progetto25zero1
Arduino with PD: Arduino Playground - PD
Arduino meets Processing: http://webzone.k3.mah.se/projects/arduino-workshop/projects/arduino_meets_processing/instructions/index.html
VVVV: http://vvvv.meso.net/tiki-index.php?page=arduino01
Director: Arduino Playground - Director
Of course, we can also use more info, so sign up for the playground and share your experience:
http://www.arduino.cc/playground/Main/LoginForm