Engine does not turn, initially it sounded as starter was stuck tried bump starting but to no avail. Also noticed following when turning key headlamps flashed although lights not on, electric windows and wipers will not work. somebody told me you cannot bump start bmws, is this true

If the battery is good and charged up to read at least 12.5 Volts, then it sounds like the vehicle anti-theft security system is preventing you from starting the engine.

Sears Voltmeter to check battery voltage:
http://www.sears.com/shc/s/search_10153_12605?keyword=digital+multimeter&gobutton.x=0&gobutton.y=0&gobutton=find

How to change a battery:
http://www.ehow.com/how_512_replace-car-battery.html

probably the battery ring up a LOCAL INDEPENDENT garage and ask them