There is no aux-in on models prior to either '02 or '01, I can't remember which; regardless, there is no aux-in on a 1997. As far as removing the head unit, if you still want to, check the Business CD Installation article on BMWtips.com under the Tips and Tricks section.
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>.
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