because 6.22 is directx8 not 9 this shader will not work(because it's HLSL). A new shader would have to be written to use ps 1.1-1.4 in assembler. It probably wouldnt work though, as there is no clip function in the lower shader versions..you need to render the terrain manually in a dll with a clip plane.

Your best solution is to go to 6.31.. you won't regret it.