A recent project of mine might help. It was set up to control a bunch of Arduinos hooked up to a Pi from Isadora:
https://github.com/kfriedberg/bridgepi
The project turns the Pi into a rather single-purpose device, but the following might make Raspbian do the same thing.
First, get the serial number of your Arduino. Either plug it into the Pi and look towards the end of the output of the 'dmesg' command, or plug it in to Windows, go to the device details and find the Device Instance Path (it's the long hex number after the last backslash).
Next, install socat ($ apt-get install socat)
Then, make a file /etc/udev/rules.d/90-arduino.rules (90-.rules, really). The file should contain the following line, adjusted for your situation:
SUBSYSTEM=="tty", ATTRS{serial}=="64131383331351411041", SYMLINK+="tty_arduino" RUN+="/sbin/start-stop-daemon -S --exec socat --background --pidfile /var/run/tty_arduino.pid --make-pidfile -- -d -d -ly TCP-LISTEN:4571,forever,fork /dev/tty_arduino,b9600,raw,echo=0"
Reboot, and whenever the Arduino's plugged in you should be able to contact it on port 4571 of the Pi.
If you've got multiple Arduinos, the rules file can have multiple lines. Each line needs to have a different value for the serial number, a different name for "tty_arduino" (careful, that's in 3 places on each line), and a different port on TCP-LISTEN.