Hey, nice car!! I got one of them 320i's heh
As for the door cards, just unscrew the two screws by the door handle (after yo pull off the little covers), they're a funny star screw. Then unscrew the little black thing on top of the door card that is used to lock the door.
Now just start pulling, start on one edge and work your way around. They should just pop out pretty easily.
The clips are really shit, especially when they're this old and brittle. You probably won't break any taking the door cards off but they break when you go to put them back in, don't align the hole-clip correctly and push
They're very cheap but got to get them from a BMW dealership.
I recommend you also download the BMW bentley manual. Its got everything in it that you might ever need pretty much.
Good luck and let me know if you got any other questions...