I did change rear passenger side reg for 2001 330i, two more doors coming. Make sure you disconnect your battery assuming you have a airbag at the door you are fixing. It took me 2 hours but next time it should take me less than 30 min.. I don't know how different with X5 but the main factor would be overcoming the fear of messing up a expansive car and getting your hands messy. Fortunately my X5 is still under warranty.