" Use lo poly figures or, if you have something simple like people running around, render a single person as a video clip, then use that video clip as texture on 100 simple squares." Good solution, but it could be problematic. What happens if you need the camera animated to where the tops of the squares would be within the range of sight? It would kill the illusion of depth. The low poly figures are probably the best way to go, but if you need an animated crowd, you're in for a possible animation nightmare. I think the best advice is to animate and render the crowd in "layers", and composit the final shot in a good video editor. There's a mat material available (by Stewer I believe) that will assist in compositing. Either that, or outsource the project to a more capable software. Again, it all depends on your needs. If this is a professional project that you're on a budget with, I'd avoid using Poser for such a thing. You'll be dealing with all kinds of workflow and stability issues when you start getting that deep with figures, and it could put you totally out of your timeframe.

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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.