Creating terrains

Dear IMG Team,

I am trying to create simple terrain application, few hills and such. I could get managed to make it in Blender, convert to POD and then load in my game. Now I want to display sphere object, based on the terrain's height at particular position. So I simply move the sphere across the terrain and want it to go up and down, depending on the landscape height.

Terrain doesn't necessary should have a texture, it could be just some material.

Assume that I have a terrainMesh and a sphereMesh:
I want to display my sphere at some X1, Y1, Z1 position on the terrain. X1 and Y1 I can set myself based on the keyboard input, but what about Z1, how can I calculate the value using terrainMesh?

Thank you.