since you're using a mac, are you using a two button mouse or a single? (two with a wheel would be the best) there might have been a click (right, left, middle... something!) lost in translation between pc and mac. i don't have the tutorial myself so i don't know what he says while he's doing it.

one thing i suspect is that you might have accidentally never even attached your material to the plane.

just to be sure, with the hypershade still open, left click on your plane. hit the 6 button. like you said, you won't see anything. after that, in the hypershade, right click on your lambert and you should see an option in the marking menu that says 'assign material to selection'. that should make sure your material is actually attached to the plane.

since 6 (display hardware shading) was already pressed, your head should appear on the plane. if not, then there's other things we can look at.