Terrain normals?

Hey,

I've been trying to get a selection method into my game, basically just using gluDisk to show that an object is selected, but one thing is pestering me and thats that the circle cuts into the terrain as it is always horizontal, is there a function lying about torque that gets the normal of the polygon that the player is standing on? so I could apply it as a rotation somehow to my disk?? If it is possible! Thanks for any help!