no problem, there are no stupid questions. i am glad to be of help. :wink
the headliner is the roof of your interior. if you are inside, look above you. you should see a small square box in the center. just pry that open from the corner and see if you have the motion detector in there. if not, then you do not have the alarm system.
i have posted in your other thread, so i'll post again.
if you choose to go with the factory alarm, you should go to http://www.pacificbmw.com
. they have the best prices on OEM parts.
another alarm system that is good for BMW's, is the Stellar system. you can find that at http://www.bavauto.com
the factory alarm system is relatively easy to install, so i've heard. i haven't installed one on mine yet. can't wait to get it. i am sure that the Stellar system installation is about the same, not sure.