Old Gradient warp tool

Hi,

I am trying to find a technique used in early photoshop days (6.0) which I am pretty sure was called gradient mapping. It involved saving an image in greyscale and applying it as a gradient map to another image that would warp the new image according to grey values. The example tutorial I remember doing was of a rock wall and using that as the gradient map, applied it to a flag image on the layer above so it looked like the flag followed all the curves/cracks of the rock wall. Does anyone know if this is still achievable at all?