Aaah I forgot about sailwinch type servos. If yours (a link might be nice as we here can’t read minds) is a typical analog servo, then it works like a typical 0-180 servo. Except that a 180 degree command will get you 720 degrees. And a 90 deg command gets you 360 degrees. So all you need to do is use the standard library as shown on that page and map the 0-360 degrees of compass angle into the 0-90 degrees of servo command. To restate the obvious, the servo command is the compass reading/4.
If your servo uses an extended pulse width to get the 0-720 degrees of motion, then the same logic as above applies and you can command pulsewidths, in usec, instead of degrees.
See if you can follow the example here.
http://arduino.cc/en/Tutorial/Knob