To create displacement maps from zBrush for the Daz figures, you first need to prepare the figure the same as you would for painting, as the figures have multiple UV maps and zbrush can handle only one UV map at a time.  If you look at my tutorial on painting Daz figures, the first part tells you how to prepare a figure so that the UV maps/material regions are easily selected in zBrush so that texture or displacement maps may be exported. Once you have your figure prepared and saved, you can import it into zbrush for displacement creation.

For my example I only wanted to use the head/face material, so I CTRL+SHIFT clicked on the face sothat it was selected, and all other material/UV groups are hidden. Then I went to Geometry palette and clicked DelHidden to delete all the hidden mesh. It isn't necessary to delete the hidden mesh, but it is something I prefer to do.

Next you should store a copy of your untouched mesh before you do any dividing or sculpting.  Go to the Morph Target palette and click on StoreMT.  You will need this original mesh when you want to create your displacement.

In your Geometry palette, click on divide a couple times to subdivide your mesh. Use your tools to create your displacement. Note: displacement is for fine details. Large mesh changes should be created as morph targets instead of displacement.

When you are ready to export your displacement, return to subdivision one (SDiv slider in Geometry palette all the way to the left). You will probably notice that your base mesh has distorted a little because of your scultping. This will interfere with your displacement map creation, so you want to return your level one mesh to the original. Luckily you saved a copy (storeMT). Making sure you are at subdivision level 1, go to the Morph Target palette and click on Switch. This will switch your stored original mesh and the current level 1 mesh.  No you are ready to create your displacement map.

In the Displacement palette, you set your map size (DPRes). In the image above you can see I have it set at 1024, with Adaptive turned on. Click Create DispMap and you will see that a new Alpha has been added to your Alpha palette.

Make sure this alpha is your current alpha, as shown in my image above, then select the DE Options in the Alpha menu.

If you have Poser 7, Poser Pro, or Studio you can use 16-bit displacement maps and can use the setting above. Make sure all the other maps have the Status set to 'off' unless you want to create multiple types of maps. If you have Poser 6 you can use D8 with similar settings to create an 8-bit map. Click on Export current to save your map.

With Studio you can use the map as-is, because Studio uses medium gray as the neutral mid-point. With Poser, you will need to use a map node on the displacement map as Poser sees black as neutral. If you use the map as-is in Poser, your character will puff up like a marchmallow because the gray will cause displacement, and you probably don't want that. ;)

Apply your map, and render with displacement turned on.