Displacement maps...

create a color node, eg file... under color balance, check Alpha is Luminance. Connect the outAlpha to displacement of a Displacement node. Connect displacement node to displacement map within the shader's parent... not to the blinn or lambert or phong, but to (I don't know the terminology) the node that the shader is connected to... you'll have to view all connections in the hypershade view to find it. Anyway, once you've done that, to change the distance that black and white displace, you change the file node's alpha settings within the color balance tab.