First off, Welcome to the board!! 
![Welcome    [welcome] [welcome]](/images/smilies/icon_smile_welcome.gif) 
 
The best way to get a key for a 1997 318i would be to go to your dealer and order one. 
I needed a replacement master key for my car when I got it b/c the original one was so worn that it wouldn't work properly in the ignition.  I was originally trying to find one on ebay, and then someone pointed out to me that the key is not cut with a regular key-cutting machine (I think it's laser cut?). So I just went to the dealer. It was $28.00 for the master key and sub-keys were less than $20. Not too bad. 
Good Luck,
 Sean