make sure your bringing up the right mesh, the stalactites.mesh, then add that so you will see a big base white stalactite structure. Then you will type in the material box below the mesh box limestone <nothing else, no .mat, /mat limestonemat, just plain limestone
Now, you will see a little arrow just above the right side of the material box. It should have a number 1 and a > arrow. Make sure you click on that and type in limestone again! These things can be textured with the rock meshes already in game as well, just mix and match the rock types to create some very interesting ones. In the picture on the front posts I put both a limestone textured stalactite and the other one is textured with different rock mats. Same goes for other wombat stuff, check the ( 1> ) to be sure you are putting textures on ALL the parts of the mesh.