I'm not sure if you know, but usually there is more than just the head unit. I'm not familiar with how BMW systems work, but in the Acura TL there is the head unit, a black box in the trunk that actually contains the brain, and then a small stubby antenna. PLEASE take pics along the way once you get this project going, and if it works maybe you could write a tutorial...because I also have a '97 540i and this interests me. May be a future mod. Thanks!
Anyone who ever buys used cars online, anyone even THINKING of starting a "Is this deal too good to be true?" thread, anyone who wants to be more educated about protecting themselves must <a href='http://www.carbuyingtips.com/fraud.htm' target='_blank'>read this</a>.
<img src='http://www.3xmk.com/mrogers-files/forums/bmw/bmw_sig_small.jpg' border='0' alt='user posted image' />