Poser ProPack and up. For Poser users, the Dynamic Constraints that Brainmuffin explained for A;M above are possible in Poser. It works slightly differently. You need to have morphs in the breasts, such as up-down/left-right, or if you have a ponytail it needs morphs for moving. You animate your entire scene, ignoring those movement morphs. After you have finished animating your scene, run the Python script called Jiggles (by Ockham, available in freestuff). You can set the amount of movement, gravity, momentum, inertia, etc, for each morph. Not as easy as A:M, and not for beginners, but the effect looks good and worth the effort.

Your specialist military, sci-fi, historical and real world site.