Since you exported from ZBrush the map is most likely flipped vertically so you need to flip it back either in photoshop or re-export it from Zbrush with the flip Y on, or you can do it in Maya through the texture placement node (which gets automatically created with the texture node if you push the checker button in the Bump Mapping line of your material).
I dont know how much you know but I'll try to cover as much as I can.
Viewing your map in the viewport is the easy part, rendering it is a bit more involved.
There are a lot of ways to navigate through the nodes, this is one
Go to the material attributes for your new material, click on the checker box in bump mapping, create a file texture. Open the attributes for the bump node and where it says "Use as Bump", click and choose "Tangent Space Normals" from the popup.
Now turn on High Quality Rendering on your Viewport settings, and this pretty much wraps it as far as watching your normal map in hardware shading...
If you want to render this, things get more complex, you have to use a specific and pretty hard to do by yourself shading network on which you plug the map and then connect that to the bump of your material. Try google, if you have no luck pm me to send you the network (in .ma format so you can import it), I dont have it on this computer right now, and I can't remember the exact site from which I got it. I had thought of writing a script to produce the network but since I could always import it I didn't bother.