is there anyway to reduce the polys down?

Yes, most modeling programs have some sort of polygon-reducing function. The results are rarely as good as one might hope, though.

How hard is it to re-bone the meshes and what is involved in translating it.

Depends upon the figure and the software. Fairly simple to set up for something like the Half-Life 1 engine, using MilkShape's bone system (which resembles Poser's Setup Room). More complex if the engine has advanced features like weighted vertices. It's not the actual process of re-boning the mesh that's time-consuming; it's the prolonged period of tweaking the settings afterward to get the best results.

As far as translating is concerned, as I mentioned earlier, nothing else uses Poser's bone structure, and to the best of my knowledge, no one has really attempted to write a conversion utility that can translate it to other systems.

What about exporting into discreets gmax?

You can load the mesh into gmax, but not the skeletal structure. And aside from Quake, Unreal, and a few simulators, there aren't many other game formats supported by gmax yet.

Some utilities and websites you might find helpful:

chUmbaLum sOft, home of MilkShape 3D
Caligari.com, home of gameSpace
LithUnwrap and Ultimate Unwrap3D (lots of game formats supported)
polycount (game model central)