One way to get sharper edges in Poser is to sub-divide your bevels. In the frist picture above, I've beveled a cube; in the second picture, I subdivided each bevel face into two smaller faces (the highlighted lines) without changing their angle. The extra edge causes the spline-based smoothing algorithm in Poser to flatten the curve at the corner, resulting in a sharper edge, at the expense of a few more polys.

Also, make sure you have "smooth polygons" unchecked for your object. That feature applies additional curvature to the edges of the object, significantly rounding edges. Good for organic shapes, not-so-good for furniture and such.