well, of course it is not allowed to use ripped graphics (like Zelda-, Sonic- or Super Mario-sprites) in a game which is meant to be sold.
but how is it with homebrewed games? tiny little hobby productions, never meant to make profit? i think it is forbidden, too, since it is copyrighted material. but i also think that there is little risk for the homebrewer using the graphics, because the big companies mostly don