http://z4-forum.com/forum/viewtopic.php?f=28&t=1071
really simple procedure.
the hardest part in my opinion was getting those stupid fender well clips out in step 1. mine did not want to budge so i ended up breaking them off and replacing them with new ones. they were like 50 cents each. once those things are off the rest is pretty simple
also just a heads up, if you plan on opening your headlights to do any mods to it, unfortunately there is no way of seperating them without cutting the clear plastic from the back plastic. they do not come apart with a heat gun or sticking them in the oven like most headlights do. just giving you a heads up so you dont waste your time trying to get them apart