not sure how large you are talking about, and is it a film (moving) or still (slide) projector? You might use a piece of scrim and project on that. Depending on where you want to set up, and again how large, you can use plexiglas and do it sort of like a peppers ghost.
"Project" water under the head! There you go! It's floating!
Or put a beanie on the head with a turning prop on the beanie and the noise of the projector could be the noise of the engine turning the beanie's prop!
Sound and motion all in one effort.
well you wont get a 3-dimensional image or anything if you try it like in the video i linked to in my post...
anything more specific? you want a giant head? a small head? something see-thru? something solid?
the fog-screen effect is pretty convincing. if you dont like it then i dont have too many more ideas on how to use a projector... need more info please!