A couple of other comments related to turntable isolation. You basically have two sources of vibration - vibration or shock from people walking/dancing/jumping on the floor, and vibration generated by the music coming out of your speakers.
For floor vibrations, wall-mounting of the turntable is a great cure. The foam pad idea also helps. Further, adding mass to the "suspended" turntable will help the isolation, and will also lower the resonant frequency of the turntable's vibration, ideally to below audibility. Think of the turntable as a mass, connected by a spring to another vibrating mass (the floor, via whatever tables or stands are in between). The pad effectively softens the spring, while adding mass to the turntable makes the mass on the end of the spring higher. Both serve to lower the frequency of vibration, and isolate the turntable from the vibrating floor.
Same basic argument applies to the vibrations from the music, except that these are (or may be) coming via the air. As a result, wall-mounting probably doesn't make a difference, nor does a pad underneath the turntable. But, a more massive turntable still helps. Also, if the low-frequency music vibration is coming through the floor (from a sub-woofer that is standing on the floor, say), then the approaches mentioned above will still help. In any case, you are talking trial and error.
