I live in NYC apartment/condo. Fortunately on the top floor. First thing I did was just as Jeffjarvis did,,,let them know you care and that they should contact you if it gets too loud. At minimum you should have a large area rug (with a carpet pad) where your rig is located and make sure you decoupled the speakers from the floor/carpet. If your setting a HT system, I advise you not to wall mount your surround speakers. I set up my living room so that the speakers face into my living area not towards the adjoining walls. Last, if you use a subwoofer, you may want to put it on something like an Auralex Gramma pad. If that doesn't work for you try a Buttkicker. Right now I'm looking into sound decorative acoustical panels from www.acousticalsolutions.com. You may want to pursue that option as well.
Good Luck.
Good Luck.