If you cannot register respect. not log in, then maybe the previous owner had registered there with your VIN number.
I registered there about 3 years ago and could not log in. Finally I called BMW Munich headquarter and asked them why I cannot log it. They told me that my VIN was already registered by someone and he had a passowrd registered. Had mentioned my full VIN several times on some boards, so probably someone has used it to register under that number. They gave me another password after they confirmed that I was the real owner of the car. Anyway, not so interesting for car owners of past models. Only owner manuals of present models can be downloaded there for example. And there is also no parts list.

That is here online
http://www.realoem.com/bmw/select.do