The data you're getting does indeed remind me of sampling at the wrong baud rate, although I know that's not much help.
"g" is probably just the byte 007, which you can send to your device (assuming the baud rate is fixed!) with
imu.print(7, BYTE);
Mikal
EDIT: Hey, according to the Sparkfun datasheet (http://www.sparkfun.com/datasheets/Sensors/DataSheet-6DOF-v4-Rev1.pdf), the default baud rate is 115200. See section 4.1. That means you can't use it with NewSoftSerial. What I would do in this case is connect the IMU to the hardware serial and then add an LCD screen or some other serial monitor(connected with NewSoftSerial) for debugging and menu processing.