This is the node configuration I'm using for getting Normal Maps to work within Blender.

This simple test map was done in Zbrush and exported out as a .tif file. If you're building Normal Maps in Z and exporting for Blender, you MUST have the following options enabled within the Multi-Map Exporter:

FlipV
Tangent
SNormals

The top node path is the diffuse / color map, while the bottom path is the normal map. Use the strength slider on the Normal Node to dial up / down the effect.