   About Displacement Mapping with CG..
  I'm trying to use Displacement Mapping to render the realistic water surface with ripple simulation.My idea is to first caculate render the Height Map into a texture in Fragment Shader.And then in the next frame,I use VTF to fetch that texture and render the height in the Vertex Shader.But my problem is I donno how to pass that texture from Fragment Shader to Vertex Shader...Who can help me...Or is there any better way to do this??It's cg I'm using in case that helps~   
  Surely you just bind the sampler you rendered to for the displacement map to the required texture stage and reference it in the vertex shader?  