Those gadgets are useful for orientation, which is important for aircraft but not very useful in an automobile, unless you are interests in observing the vehicle rolling over.You'd be better off looking at GPS.
I am working on a project with a friend from school and we are looking for possible position estimation algorithms for an IMU. We are using the 9DOF Razor IMU from Sparkfun which has a 3-axis accelerometer, 3-axis gyroscope, and a 3-axis magnetometer and are look for some suggestions on algorithms or helpful resources. We have tried a variation of DCM that has been off by miles with less than a minute drive and does not even remotely match the shape. We realize that the measurements will have a decent amount of error no matter because we are integrating the accelerameter measurement twice and amplify the error a great deal but we are just trying to get something a rough estimate that is in within an order of magnitude, and has a shape somewhat resembling the actual path.