Hi to everyone,first i excuse for my crappy english(i'm italian),then i go to the point;yesterday a friend gave me a brillant idea

,"why don't you make a rocket launcer that shoots heads?",(he say me also the sound effect that this item woul be do).at first i thinked was a joke,but in the night i've got to work on this;unfortunatly i'm a complete cathastrophe to use the halo tools,but i think that the things to do are these:
-make a 3d model of the head,with correct proportions(i've thinked to import a marine model into a 3d editor,cut off his head and import it at the place of the rocket projectile)
-replace the fire effect sound of the rocket launcher
uhm,it would be all here,but i don't know from wich part start

,please help me!