I did it. Did the AC condensor as well while I was in there because if the compressor went bad, often times you can get parts clogging the condensor. I used an ebay condensor i found for $100 and its been problem free for over year now. Used all new o-rings on all the lines as well got them from germanautoparts.com. It was tough to get to the bolts on the compressor, but it wasn't nearly as hard as other jobs I've done on the car. The most important step probably was flushing the AC system. You'll have to buy a bottle of AC flush, hook it up to a compressor with like 100 pounds and blow through the AC lines to get any random crap out of the system. It makes an absolute mess, but you'd be amazed what came out on my rag. If not it could ruin your condensor and new compressor. Youtube was my best friend for learning AC flushing procedures as well as AC general procedures. Its not much different on a BMW than it is for a chevy pickup, so a lot of information out there. I recommend reading up as much as you can, just on AC systems in general.
When I was finished I took it to the shop and for 100 bucks, the guy charged it, put in the correct amount of oil, and pulled a vacuum on the system. It would have been $100 for the vacuum manifold system and refrigerant so I just let him do it.