The question is, do you absolutely NEED to do this directly in Poser. Sure, it can be done... but that doesn't mean you have to do it. Poser isn't the best software for such a task. Creating a still scene with 100's of figures is one thing, but for animation is another. Do you have any other 3D software? There's a variety of ways you could achieve this in other software a lot easier than in Poser, depending on what you have available and what your budget is. Is this a serious project or something just for fun? Since this is for animation, how REALISTIC do you need the crowd to be (do you need them animated as well, with random realistic movements)? There is software out there specifically designed for such things, but I must warn you... it's VERY expensive, but the results are professional quality. Here's an example: Massive Software You can also do some great crowds rather easily in Character Studio for 3dsMax if you have that. It can also be done via instancing on low-poly figures much easier than you could do it directly in Poser. So I think the answer you seek depends on your needs.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.