I already posted these settings last year on http://www.3dhype.com but the explanations are in Dutch. So on request I will post the settings for rendering ZBrush displacement maps in 3dsmax v8 with mental ray. As example I am going to use the test head from ZBrushCentral.
Import the test head and convert it to an EditablePoly, set the number of subdivisions for rendering at 2. You can also use a TurboSmooth or MeshSmooth modifier to get the same result.
Then apply a material to the mesh and add a displacement map. The UV coordinates are flipped in ZBrush set the V Tiling to -1.
The displacement map is positive and negative in ZBrush, 3dsmax has default only positive displacement. To solve this go to the Output panel of the displacement map and set the output curve to -1…1. (You can also use -0.5 … 0.5).
Set mental ray as renderer and check that the displacement is on. Default the edge length is set to 2. This however causes loss of detail. Set it to 0.5 this will subdivide the mesh to tiny triangles with an edge length of a halve pixel. Of course this will have impact on the rendering time but it results in the best displacement mapping results.
Now you can render the mesh.