This is example Arduino code that allows you to print raw accelerometer, gyro, and magnetometer data. The original library came from i2cdevlib.com and was based on the very similar MPU-6050, which only used an accelerometer and gyro. The MPU-6050 device library was modified to include raw magnetometer data for the MPU-9150.
To use the library, copy both I2Cdev and MPU6050 into your libraries folder in your main Arduino directory. If you don't have a folder called libraries, create one and drop both files in there. Now you can goto the example sketch named MPU9150_raw (in MPU6050 -> Examples), open and run the main .ino file.