There are a number of websites that will give you information about the build date of your bike and the OEM accessories.
The most comprehensive is:
http://www.bmwarchiv.de/vin/
You simply enter the last seven numbers of your VIN and it will give you the day of manufacture, factory colour and all of the OEM equipment it left the factory with.
Other useful sites are:
http://www.bmw-z1.com/VIN/VINdecode-e.cgi
http://www.realoem.com/bmw/select.do