The package ros_arduino_bridge is probably what you are looking for if you want to combine Arduino and ROS. See also related blogpost by the author here.
Also, I suggest picking up ROS By Example - Volume 1 as a general introduction to ROS. While not focused on Arduino, it is the best ROS introduction I know (and accidentally, is written by the same author as ros_arduino_bridge).
EDIT:
I should also point out that ros_arduino_bridge is basically a ROS driver for Arduino - it allows you to control your Arduino board from within the ROS framework. You will still need an additional, higher-end system to run the actual ROS nodes (Arduino hardware is not sufficiently powerful for that).