Your only issue with the Inter-Integrated Circuit (I2C) communications is... none of the lines from the processor that do I2C are routed outside the board!
If your working on an non-FIRST project, then definintely you can use I2C, however, on the FIRST RC you'll need to use PWM.
According to the website that you ordered this from, the PWM signal updates at anywhere from 66ms - 102ms (or 9.8 - 15.2Hz, slower the closer you get to 359.9degrees).
If you need help doing PWM pulse timing, just give me a yell, didnt know if you just wanted advice with which way to go or what. You can check
this post to see if it will help you any, but can't remember if i said much on pwm timing here. Again, if not, just give me a yell back on this thread and i'll be happy to help.
By the way just for my curiosity, what's this compass for exactly? Why do you want to know which way your robot's going? Arent you worried about flux fields from motors and such in your robot throwing it off?
-q