You can search for the diagram on http://getbmwparts.com/
I haven't drained the radiator before on my car so someone else will need to chime in here.
When I have done radiators in the past, I've always cut the hose and drained it. It makes it easier to remove the hose when it's cut in half.
Taz... My favorite BMW so far.
Sport, Cold weather, Logic 7
19" Miro M6 Wheels w/competition stems
MGP Claiper Covers (BMW)
Dension Gateway 500 and Audio Video Router
AC Schnitzer pedals
Carbon Fiber Di-Noc Trim
5W White Angel Eyes