The extrude thing kind of got me confused too at first because I'm using 3DStudio Max and it has an "extrude" function that is quite differnet. It mounts an identical polygon on top of the original and does the sides too. it looks like you're putting a brick on top of the first one. Like in the picture, the box on the right is the original and the box on the left is the same one with the top polygon extruded. It doesn't move it by itself, it creates a bunch of new polygons. CoL