If you go to BMW, they'll just sell you a new or rebuilt tranny ($4-7k). If you can get the car moving with the above, it's a $700 fix. There's a small (5mm) ball plastic-like bearing that can swell or shrink. We're talking 1mm will make the difference between go and no-go.

I took it to a place in Menlo Park, CA call Karl Schmit's (from memory, so....) that specialized in rebuilding transmissions; mostly Benzes, but also does BMW. He's been written up in Star (Benz's equivalent to Roundel magazine) a couple of time. This guy is good and many garages send their tranmission to him. He had about 300 rebuilt trannies onsite. He rebuilt a section of the my tranny for $700 (It's about $250 just for the tranny fluid).

I am wandering... Try reving the engine in drive and see if it goes.