Hi mate I have done this job last week. here is the steps that you need to follow.
you have to remove both AC and serpentine belts to do this job. the whole job takes about couple of hours.
1) First remove the air filter and its housing, MAF sensor. Removing these gives you better access. You dont have to remove if you can with them in place.
2) To remove alternator first disconnect the battery (obviously), then undo the cable that is connect to the back of the alternator with a 13in bolt. Alternator is held in place by two bolts to the alternator mounting device. one on top and the other on bottom. see the link below for the position of two bolts.
http://www.realoem.com/bmw/showparts.do?model=AL32&mospid=47631&btnr=12_0607&hg=12&fg=22
you should also remove the power steering fluid tank because it comes in the way of the bottom bolt. Spray WD40 at the edges where alternator is attached to its mounting device. spray on top and bottom as well. Make sure you dont spray on to the inside of alternator. wait for 5min.
Slide a strong screw driver/crow bar between the gap of alternator and its mounting device from the top and gently push out wards towards clock wise direction. Dont use brute force. this shouls slide out the alternator.
3) next remove the alternator mounting device which is held in place by 6bolts. see the link below
http://www.realoem.com/bmw/showparts.do?model=AL32&mospid=47631&btnr=12_0572&hg=12&fg=21
4) then undo the 6 10mm bolts on the oil filter housing device.
5) make sure you also replace the two o rings. Its part 5 in the below link. one ring towards the engine block side and the other towards the oil filter housing. once you replace those two the bush should fit snuggly on both ends.
http://www.realoem.com/bmw/showparts.do?model=AL32&mospid=47631&btnr=11_1568&hg=11&fg=30
follow the reverse to fit back everything. try to sand the edges of alternator bracket and alternator where it attaches to the bracket.
Hope this is helpfull.
Good luck