hmmm... I also see a styles/default/xenforo/xenforo-smilies-sprite.png file. I reckon I has to check it out pixel by pixel to get the x and y? Would be nice to use the existing sprite.
EDIT: using the sprite method. I likey how as I press + and - the little smilie shows up in the top right (cuz I suck at the x and y thing)