You can manually optimize any mesh by adding a edit poly, switch to edges, and enable edge loop mode from the Graphite Ribbon (if you don't have it mapped to a hotkey).  Loop Mode allows you to quickly select full edge loops by simply clicking on any edge, then CTRL+BACKSPACE to remove them.  Even on dense topology, this would be the cleanest way to optimize; assuming the mesh in question consists entirely of quads.  This should, in theory, preserve any animation baked into the character as well.  I am not familiar with Poser or PoserFusion, so this is merely speculation.

There's also a plugin called Polygon Cruncher, which does a very good job preserving all kinds of things in a reduced mesh, like UV's.  Can't guarantee it will work for you in this case, but it's another option.

http://www.mootools.com/plugins/us/polygoncruncher/3dsmax.htm

Alternatively, there are some Maxscripts which promise to retain the mesh type, and all kinds of modifiers.  This is one of them:

http://www.scriptspot.com/3ds-max/scripts/lod-creator

Here's another one for Maxscript:

http://www.scriptspot.com/3ds-max/scripts/auto-prooptimizer

If Scriptspot is currently "offline" right now for maintenance, they should return in a few hours.

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