Cone Navigation

Hi All,

This is my first mail since i have recently joined in this group. We have an application where in we create a virual room,with all the walls as polygons and floor as an formation of grid using polygons. We need to drag a texture from the GUI and place it over any wall surface or on any particular grid area onto the floor , for this a wire cone needs to indicate the location of the mouse .When my mouse moves on the floor area the cone base rests on the floor and when it goes to the walls it rests on the wall , cone should always rest on some geometry where my mouse is currently pointing to . I think some one can advice me how to calculate collisions made by cone and how to navigate in the room.