Many thanks for your advice Motordavid. Changed my battery this evening which took me about 20 minutes. Was left with some lights on the dash but followed the advice of Eurosport, on the same thread, and turned the steering wheel left/right from lock to lock and everything reset straight away.

The battery I bought was a VARTA H3. It has a higher spec than the BMW OEM and is a lot less expensive at £89.00 (about $140). Found the seller on Ebay.

I didn't realise that I had a problem with my battery until my radio started cutting out. I found a thread on xoutpost.com saying that it could be at fault and I'm please to say that replacing it has solved this problem. My old battery was installed in March 2004 so it served me well.

Make sure that you disconnect the negative terminal (black) on the old battery first then connect the positive (red) on the new one first or you might get a 'spike' which could do some damage!

With the help of xoutpost.com and Martin at bimmernav.com so far I have changed my nav from MkIII to the DVD Mk IV version and bluetoothed the hard wired phone that was in the car when I bought it. My iphone works fine with it too