I have adapted the Arduino AT90CANxx support to work with Arduino 1.0+. Also, I have moved the code to github, so that it will be easier to update. Note that the Arduino 1.0+ support is currently only alpha quality. I have compiled a few sketches, but I also have found some which currently can’t compile.
You can always download the latest version at https://github.com/lincomatic/AT90CAN
It is easiest to download the whole repository as a zip file: https://github.com/lincomatic/AT90CAN/zipball/master
Follow the instructions in the README file. For more information, see the post linked below.